diff --git a/java/com/google/gerrit/acceptance/ExtensionRegistry.java b/java/com/google/gerrit/acceptance/ExtensionRegistry.java
index 85c4c13..1e5598e 100644
--- a/java/com/google/gerrit/acceptance/ExtensionRegistry.java
+++ b/java/com/google/gerrit/acceptance/ExtensionRegistry.java
@@ -25,6 +25,8 @@
 import com.google.gerrit.extensions.events.GitReferenceUpdatedListener;
 import com.google.gerrit.extensions.events.GroupIndexedListener;
 import com.google.gerrit.extensions.events.ProjectIndexedListener;
+import com.google.gerrit.extensions.events.ReviewerAddedListener;
+import com.google.gerrit.extensions.events.ReviewerDeletedListener;
 import com.google.gerrit.extensions.events.RevisionCreatedListener;
 import com.google.gerrit.extensions.events.TopicEditedListener;
 import com.google.gerrit.extensions.events.WorkInProgressStateChangedListener;
@@ -91,6 +93,8 @@
   private final DynamicMap<ProjectConfigEntry> pluginConfigEntries;
   private final DynamicSet<PluginPushOption> pluginPushOptions;
   private final DynamicSet<OnPostReview> onPostReviews;
+  private final DynamicSet<ReviewerAddedListener> reviewerAddedListeners;
+  private final DynamicSet<ReviewerDeletedListener> reviewerDeletedListeners;
 
   @Inject
   ExtensionRegistry(
@@ -125,7 +129,9 @@
       DynamicMap<PluginProjectPermissionDefinition> pluginProjectPermissionDefinitions,
       DynamicMap<ProjectConfigEntry> pluginConfigEntries,
       DynamicSet<PluginPushOption> pluginPushOption,
-      DynamicSet<OnPostReview> onPostReviews) {
+      DynamicSet<OnPostReview> onPostReviews,
+      DynamicSet<ReviewerAddedListener> reviewerAddedListeners,
+      DynamicSet<ReviewerDeletedListener> reviewerDeletedListeners) {
     this.accountIndexedListeners = accountIndexedListeners;
     this.changeIndexedListeners = changeIndexedListeners;
     this.groupIndexedListeners = groupIndexedListeners;
@@ -158,6 +164,8 @@
     this.pluginConfigEntries = pluginConfigEntries;
     this.pluginPushOptions = pluginPushOption;
     this.onPostReviews = onPostReviews;
+    this.reviewerAddedListeners = reviewerAddedListeners;
+    this.reviewerDeletedListeners = reviewerDeletedListeners;
   }
 
   public Registration newRegistration() {
@@ -302,6 +310,14 @@
       return add(onPostReviews, onPostReview);
     }
 
+    public Registration add(ReviewerAddedListener reviewerAddedListener) {
+      return add(reviewerAddedListeners, reviewerAddedListener);
+    }
+
+    public Registration add(ReviewerDeletedListener reviewerDeletedListener) {
+      return add(reviewerDeletedListeners, reviewerDeletedListener);
+    }
+
     private <T> Registration add(DynamicSet<T> dynamicSet, T extension) {
       return add(dynamicSet, extension, "gerrit");
     }
diff --git a/java/com/google/gerrit/server/change/AddReviewersOp.java b/java/com/google/gerrit/server/change/AddReviewersOp.java
index a333ce5..cbbd01a 100644
--- a/java/com/google/gerrit/server/change/AddReviewersOp.java
+++ b/java/com/google/gerrit/server/change/AddReviewersOp.java
@@ -219,8 +219,13 @@
               .map(r -> accountCache.get(r.accountId()))
               .flatMap(Streams::stream)
               .collect(toList());
-      reviewerAdded.fire(
-          ctx.getChangeData(change), patchSet, reviewers, ctx.getAccount(), ctx.getWhen());
+      eventSender =
+          () ->
+              reviewerAdded.fire(
+                  ctx.getChangeData(change), patchSet, reviewers, ctx.getAccount(), ctx.getWhen());
+      if (sendEvent) {
+        sendEvent();
+      }
     }
   }
 }
diff --git a/java/com/google/gerrit/server/change/DeleteReviewerOp.java b/java/com/google/gerrit/server/change/DeleteReviewerOp.java
index a26f107..1e40429 100644
--- a/java/com/google/gerrit/server/change/DeleteReviewerOp.java
+++ b/java/com/google/gerrit/server/change/DeleteReviewerOp.java
@@ -202,16 +202,23 @@
             "Cannot email update for change %s", currChange.getId());
       }
     }
-    reviewerDeleted.fire(
-        ctx.getChangeData(currChange),
-        patchSet,
-        accountCache.get(reviewer.id()).orElse(AccountState.forAccount(reviewer)),
-        ctx.getAccount(),
-        mailMessage,
-        newApprovals,
-        oldApprovals,
-        notify.handling(),
-        ctx.getWhen());
+
+    NotifyHandling notifyHandling = notify.handling();
+    eventSender =
+        () ->
+            reviewerDeleted.fire(
+                ctx.getChangeData(currChange),
+                patchSet,
+                accountCache.get(reviewer.id()).orElse(AccountState.forAccount(reviewer)),
+                ctx.getAccount(),
+                mailMessage,
+                newApprovals,
+                oldApprovals,
+                notifyHandling,
+                ctx.getWhen());
+    if (sendEvent) {
+      sendEvent();
+    }
   }
 
   private Iterable<PatchSetApproval> approvals(ChangeContext ctx, Account.Id accountId) {
diff --git a/java/com/google/gerrit/server/change/ReviewerOp.java b/java/com/google/gerrit/server/change/ReviewerOp.java
index 716ac5e..12227c2 100644
--- a/java/com/google/gerrit/server/change/ReviewerOp.java
+++ b/java/com/google/gerrit/server/change/ReviewerOp.java
@@ -32,6 +32,8 @@
 
 public class ReviewerOp implements BatchUpdateOp {
   protected boolean sendEmail = true;
+  protected boolean sendEvent = true;
+  protected Runnable eventSender = () -> {};
   protected PatchSet patchSet;
   protected Result opResult;
 
@@ -42,6 +44,14 @@
     this.sendEmail = false;
   }
 
+  public void suppressEvent() {
+    this.sendEvent = false;
+  }
+
+  public void sendEvent() {
+    eventSender.run();
+  }
+
   void setPatchSet(PatchSet patchSet) {
     this.patchSet = requireNonNull(patchSet);
   }
diff --git a/java/com/google/gerrit/server/restapi/change/PostReview.java b/java/com/google/gerrit/server/restapi/change/PostReview.java
index 5002a82..5c252f4 100644
--- a/java/com/google/gerrit/server/restapi/change/PostReview.java
+++ b/java/com/google/gerrit/server/restapi/change/PostReview.java
@@ -92,7 +92,9 @@
 import com.google.gerrit.server.PatchSetUtil;
 import com.google.gerrit.server.PublishCommentUtil;
 import com.google.gerrit.server.ReviewerSet;
+import com.google.gerrit.server.account.AccountCache;
 import com.google.gerrit.server.account.AccountResolver;
+import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.approval.ApprovalsUtil;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.change.EmailReviewComments;
@@ -105,6 +107,7 @@
 import com.google.gerrit.server.change.WorkInProgressOp;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.extensions.events.CommentAdded;
+import com.google.gerrit.server.extensions.events.ReviewerAdded;
 import com.google.gerrit.server.logging.Metadata;
 import com.google.gerrit.server.logging.TraceContext;
 import com.google.gerrit.server.notedb.ChangeNotes;
@@ -187,6 +190,7 @@
   private final BatchUpdate.Factory updateFactory;
   private final ChangeResource.Factory changeResourceFactory;
   private final ChangeData.Factory changeDataFactory;
+  private final AccountCache accountCache;
   private final ApprovalsUtil approvalsUtil;
   private final ChangeMessagesUtil cmUtil;
   private final CommentsUtil commentsUtil;
@@ -206,6 +210,7 @@
   private final PluginSetContext<CommentValidator> commentValidators;
   private final PluginSetContext<OnPostReview> onPostReviews;
   private final ReplyAttentionSetUpdates replyAttentionSetUpdates;
+  private final ReviewerAdded reviewerAdded;
   private final boolean strictLabels;
   private final boolean publishPatchSetLevelComment;
 
@@ -214,6 +219,7 @@
       BatchUpdate.Factory updateFactory,
       ChangeResource.Factory changeResourceFactory,
       ChangeData.Factory changeDataFactory,
+      AccountCache accountCache,
       ApprovalsUtil approvalsUtil,
       ChangeMessagesUtil cmUtil,
       CommentsUtil commentsUtil,
@@ -233,10 +239,12 @@
       PermissionBackend permissionBackend,
       PluginSetContext<CommentValidator> commentValidators,
       PluginSetContext<OnPostReview> onPostReviews,
-      ReplyAttentionSetUpdates replyAttentionSetUpdates) {
+      ReplyAttentionSetUpdates replyAttentionSetUpdates,
+      ReviewerAdded reviewerAdded) {
     this.updateFactory = updateFactory;
     this.changeResourceFactory = changeResourceFactory;
     this.changeDataFactory = changeDataFactory;
+    this.accountCache = accountCache;
     this.commentsUtil = commentsUtil;
     this.publishCommentUtil = publishCommentUtil;
     this.psUtil = psUtil;
@@ -256,6 +264,7 @@
     this.commentValidators = commentValidators;
     this.onPostReviews = onPostReviews;
     this.replyAttentionSetUpdates = replyAttentionSetUpdates;
+    this.reviewerAdded = reviewerAdded;
     this.strictLabels = gerritConfig.getBoolean("change", "strictLabels", false);
     this.publishPatchSetLevelComment =
         gerritConfig.getBoolean("event", "comment-added", "publishPatchSetLevelComment", true);
@@ -371,6 +380,7 @@
       logger.atFine().log("adding reviewer additions");
       for (ReviewerModification reviewerResult : reviewerResults) {
         reviewerResult.op.suppressEmail(); // Send a single batch email below.
+        reviewerResult.op.suppressEvent(); // Send events below, if possible as batch.
         bu.addOp(revision.getChange().getId(), reviewerResult.op);
         if (!ccOrReviewer && reviewerResult.reviewers.contains(account)) {
           logger.atFine().log("calling user is explicitly added as reviewer or CC");
@@ -386,6 +396,7 @@
         ReviewerModification selfAddition =
             reviewerModifier.ccCurrentUser(revision.getUser(), revision);
         selfAddition.op.suppressEmail();
+        selfAddition.op.suppressEvent();
         bu.addOp(revision.getChange().getId(), selfAddition.op);
       }
 
@@ -433,8 +444,10 @@
         reviewerResult.gatherResults(cd);
       }
 
-      // Sending from AddReviewersOp was suppressed so we can send a single batch email here.
+      // Sending emails and events from ReviewersOps was suppressed so we can send a single batch
+      // email/event here.
       batchEmailReviewers(revision.getUser(), revision.getChange(), reviewerResults, notify);
+      batchReviewerEvents(revision.getUser(), cd, revision.getPatchSet(), reviewerResults, ts);
     }
 
     return Response.ok(output);
@@ -512,6 +525,35 @@
     }
   }
 
+  private void batchReviewerEvents(
+      CurrentUser user,
+      ChangeData cd,
+      PatchSet patchSet,
+      List<ReviewerModification> reviewerModifications,
+      Timestamp when) {
+    List<AccountState> newlyAddedReviewers = new ArrayList<>();
+
+    // There are no events for CCs and reviewers added/deleted by email.
+    for (ReviewerModification modification : reviewerModifications) {
+      Result reviewerAdditionResult = modification.op.getResult();
+      if (modification.state() == ReviewerState.REVIEWER) {
+        newlyAddedReviewers.addAll(
+            reviewerAdditionResult.addedReviewers().stream()
+                .map(psa -> psa.accountId())
+                .map(accountId -> accountCache.get(accountId))
+                .flatMap(Streams::stream)
+                .collect(toList()));
+      } else if (modification.state() == ReviewerState.REMOVED) {
+        // There is no batch event for reviewer removals, hence fire the event for each
+        // modification that deleted a reviewer immediately.
+        modification.op.sendEvent();
+      }
+    }
+
+    // Fire a batch event for all newly added reviewers.
+    reviewerAdded.fire(cd, patchSet, newlyAddedReviewers, user.asIdentifiedUser().state(), when);
+  }
+
   private RevisionResource onBehalfOf(RevisionResource rev, LabelTypes labelTypes, ReviewInput in)
       throws BadRequestException, AuthException, UnprocessableEntityException,
           PermissionBackendException, IOException, ConfigInvalidException {
diff --git a/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java b/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
index b79be80..96bc65d 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
@@ -27,6 +27,7 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.google.common.truth.Correspondence;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
@@ -56,6 +57,8 @@
 import com.google.gerrit.extensions.common.RobotCommentInfo;
 import com.google.gerrit.extensions.config.FactoryModule;
 import com.google.gerrit.extensions.events.CommentAddedListener;
+import com.google.gerrit.extensions.events.ReviewerAddedListener;
+import com.google.gerrit.extensions.events.ReviewerDeletedListener;
 import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
 import com.google.gerrit.extensions.restapi.RestApiException;
@@ -74,6 +77,7 @@
 import com.google.inject.Inject;
 import com.google.inject.Module;
 import java.sql.Timestamp;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
@@ -699,6 +703,61 @@
   }
 
   @Test
+  public void addingReviewers() throws Exception {
+    PushOneCommit.Result r = createChange();
+
+    TestAccount user2 = accountCreator.user2();
+
+    TestReviewerAddedListener testReviewerAddedListener = new TestReviewerAddedListener();
+    try (Registration registration =
+        extensionRegistry.newRegistration().add(testReviewerAddedListener)) {
+      // add user and user2
+      ReviewResult reviewResult =
+          gApi.changes()
+              .id(r.getChangeId())
+              .current()
+              .review(ReviewInput.create().reviewer(user.email()).reviewer(user2.email()));
+
+      assertThat(
+              reviewResult.reviewers.values().stream()
+                  .filter(a -> a.reviewers != null)
+                  .map(a -> Iterables.getOnlyElement(a.reviewers).name)
+                  .collect(toImmutableSet()))
+          .containsExactly(user.fullName(), user2.fullName());
+    }
+
+    assertThat(
+            gApi.changes().id(r.getChangeId()).reviewers().stream()
+                .map(a -> a.name)
+                .collect(toImmutableSet()))
+        .containsExactly(user.fullName(), user2.fullName());
+
+    // Ensure only one batch email was sent for this operation
+    FakeEmailSender.Message message = Iterables.getOnlyElement(sender.getMessages());
+    assertThat(message.body())
+        .containsMatch(
+            Pattern.quote("Hello ")
+                + "("
+                + Pattern.quote(String.format("%s, %s", user.fullName(), user2.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s, %s", user2.fullName(), user.fullName()))
+                + ")");
+    assertThat(message.htmlBody())
+        .containsMatch(
+            "("
+                + Pattern.quote(String.format("%s and %s", user.fullName(), user2.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s and %s", user2.fullName(), user.fullName()))
+                + ")"
+                + Pattern.quote(" to <strong>review</strong> this change"));
+
+    // Ensure that a batch event has been sent:
+    // * 1 batch event for adding user and user2 as reviewers
+    assertThat(testReviewerAddedListener.receivedEvents).hasSize(1);
+    assertThat(testReviewerAddedListener.getReviewerIds()).containsExactly(user.id(), user2.id());
+  }
+
+  @Test
   public void deletingReviewers() throws Exception {
     PushOneCommit.Result r = createChange();
 
@@ -712,21 +771,25 @@
 
     sender.clear();
 
-    // remove user and user2
-    ReviewResult reviewResult =
-        gApi.changes()
-            .id(r.getChangeId())
-            .current()
-            .review(
-                ReviewInput.create()
-                    .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)
-                    .reviewer(user2.email(), ReviewerState.REMOVED, /* confirmed= */ true));
+    TestReviewerDeletedListener testReviewerDeletedListener = new TestReviewerDeletedListener();
+    try (Registration registration =
+        extensionRegistry.newRegistration().add(testReviewerDeletedListener)) {
+      // remove user and user2
+      ReviewResult reviewResult =
+          gApi.changes()
+              .id(r.getChangeId())
+              .current()
+              .review(
+                  ReviewInput.create()
+                      .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)
+                      .reviewer(user2.email(), ReviewerState.REMOVED, /* confirmed= */ true));
 
-    assertThat(
-            reviewResult.reviewers.values().stream()
-                .map(a -> a.removed.name)
-                .collect(toImmutableSet()))
-        .containsExactly(user.fullName(), user2.fullName());
+      assertThat(
+              reviewResult.reviewers.values().stream()
+                  .map(a -> a.removed.name)
+                  .collect(toImmutableSet()))
+          .containsExactly(user.fullName(), user2.fullName());
+    }
 
     assertThat(gApi.changes().id(r.getChangeId()).reviewers()).isEmpty();
 
@@ -748,6 +811,12 @@
                 + "|"
                 + Pattern.quote(String.format("%s and %s", user2.fullName(), user.fullName()))
                 + ")");
+
+    // Ensure that events have been sent:
+    // * 2 events for removing user and user2 as reviewers (one event per removed reviewer, batch
+    //   event not available for reviewer removal)
+    assertThat(testReviewerDeletedListener.receivedEvents).hasSize(2);
+    assertThat(testReviewerDeletedListener.getReviewerIds()).containsExactly(user.id(), user2.id());
   }
 
   @Test
@@ -766,30 +835,38 @@
 
     sender.clear();
 
-    // remove user and user2 while adding user3 and user4
-    ReviewResult reviewResult =
-        gApi.changes()
-            .id(r.getChangeId())
-            .current()
-            .review(
-                ReviewInput.create()
-                    .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)
-                    .reviewer(user2.email(), ReviewerState.REMOVED, /* confirmed= */ true)
-                    .reviewer(user3.email())
-                    .reviewer(user4.email()));
+    TestReviewerAddedListener testReviewerAddedListener = new TestReviewerAddedListener();
+    TestReviewerDeletedListener testReviewerDeletedListener = new TestReviewerDeletedListener();
+    try (Registration registration =
+        extensionRegistry
+            .newRegistration()
+            .add(testReviewerAddedListener)
+            .add(testReviewerDeletedListener)) {
+      // remove user and user2 while adding user3 and user4
+      ReviewResult reviewResult =
+          gApi.changes()
+              .id(r.getChangeId())
+              .current()
+              .review(
+                  ReviewInput.create()
+                      .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)
+                      .reviewer(user2.email(), ReviewerState.REMOVED, /* confirmed= */ true)
+                      .reviewer(user3.email())
+                      .reviewer(user4.email()));
 
-    assertThat(
-            reviewResult.reviewers.values().stream()
-                .filter(a -> a.removed != null)
-                .map(a -> a.removed.name)
-                .collect(toImmutableSet()))
-        .containsExactly(user.fullName(), user2.fullName());
-    assertThat(
-            reviewResult.reviewers.values().stream()
-                .filter(a -> a.reviewers != null)
-                .map(a -> Iterables.getOnlyElement(a.reviewers).name)
-                .collect(toImmutableSet()))
-        .containsExactly(user3.fullName(), user4.fullName());
+      assertThat(
+              reviewResult.reviewers.values().stream()
+                  .filter(a -> a.removed != null)
+                  .map(a -> a.removed.name)
+                  .collect(toImmutableSet()))
+          .containsExactly(user.fullName(), user2.fullName());
+      assertThat(
+              reviewResult.reviewers.values().stream()
+                  .filter(a -> a.reviewers != null)
+                  .map(a -> Iterables.getOnlyElement(a.reviewers).name)
+                  .collect(toImmutableSet()))
+          .containsExactly(user3.fullName(), user4.fullName());
+    }
 
     assertThat(
             gApi.changes().id(r.getChangeId()).reviewers().stream()
@@ -832,6 +909,15 @@
                 + "|"
                 + Pattern.quote(String.format("%s and %s", user2.fullName(), user.fullName()))
                 + ")");
+
+    // Ensure that events have been sent:
+    // * 1 batch event for adding user3 and user4 as reviewers
+    // * 2 events for removing user and user2 as reviewers (one event per removed reviewer, batch
+    //   event not available for reviewer removal)
+    assertThat(testReviewerAddedListener.receivedEvents).hasSize(1);
+    assertThat(testReviewerAddedListener.getReviewerIds()).containsExactly(user3.id(), user4.id());
+    assertThat(testReviewerDeletedListener.receivedEvents).hasSize(2);
+    assertThat(testReviewerDeletedListener.getReviewerIds()).containsExactly(user.id(), user2.id());
   }
 
   @Test
@@ -964,4 +1050,36 @@
       return Optional.empty();
     }
   }
+
+  private static class TestReviewerAddedListener implements ReviewerAddedListener {
+    List<ReviewerAddedListener.Event> receivedEvents = new ArrayList<>();
+
+    @Override
+    public void onReviewersAdded(ReviewerAddedListener.Event event) {
+      receivedEvents.add(event);
+    }
+
+    public ImmutableSet<Account.Id> getReviewerIds() {
+      return receivedEvents.stream()
+          .flatMap(e -> e.getReviewers().stream())
+          .map(accountInfo -> Account.id(accountInfo._accountId))
+          .collect(toImmutableSet());
+    }
+  }
+
+  private static class TestReviewerDeletedListener implements ReviewerDeletedListener {
+    List<ReviewerDeletedListener.Event> receivedEvents = new ArrayList<>();
+
+    @Override
+    public void onReviewerDeleted(ReviewerDeletedListener.Event event) {
+      receivedEvents.add(event);
+    }
+
+    public ImmutableSet<Account.Id> getReviewerIds() {
+      return receivedEvents.stream()
+          .map(ReviewerDeletedListener.Event::getReviewer)
+          .map(accountInfo -> Account.id(accountInfo._accountId))
+          .collect(toImmutableSet());
+    }
+  }
 }