diff --git a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractHeartbeatRequestManager.java b/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractHeartbeatRequestManager.java
index 17e2b2609c6ec..4f47c8591145b 100644
--- a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractHeartbeatRequestManager.java
+++ b/clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractHeartbeatRequestManager.java
@@ -432,6 +432,22 @@ private void onErrorResponse(final R response, final long currentTimeMs) {
                     "subscribe. " + errorMessage));
                 break;
 
+            case GROUP_ID_NOT_FOUND:
+                // If the group doesn't exist (e.g., member never joined due to InvalidTopicException),
+                // GROUP_ID_NOT_FOUND should be ignored - the leave is effectively complete.
+                // When a leave heartbeat (epoch=-1) is sent, the state transitions synchronously
+                // from LEAVING to UNSUBSCRIBED in onHeartbeatRequestGenerated() before the request is sent.
+                if (membershipManager().state() == MemberState.UNSUBSCRIBED) {
+                    logger.info("{} received GROUP_ID_NOT_FOUND for group {} while unsubscribed. ",
+                            heartbeatRequestName(), membershipManager().groupId());
+                    membershipManager().onHeartbeatRequestSkipped();
+                } else {
+                    // Else, this is a fatal error, we should throw it and transition to fatal state.
+                    logger.error("{} failed due to unexpected error {}: {}", heartbeatRequestName(), error, errorMessage);
+                    handleFatalFailure(error.exception(errorMessage));
+                }
+                break;
+
             default:
                 if (!handleSpecificExceptionInResponse(response, currentTimeMs)) {
                     // If the manager receives an unknown error - there could be a bug in the code or a new error code
diff --git a/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerHeartbeatRequestManagerTest.java b/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerHeartbeatRequestManagerTest.java
index 9063ae5ab5bf4..3ef1d712c9667 100644
--- a/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerHeartbeatRequestManagerTest.java
+++ b/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerHeartbeatRequestManagerTest.java
@@ -429,6 +429,57 @@ public void testFailureOnFatalException() {
         verify(backgroundEventHandler).add(any());
     }
 
+    /**
+     * Test that GROUP_ID_NOT_FOUND error while unsubscribed is not a fatal error.
+     * This can happen when the consumer never successfully joined the group
+     * (e.g., due to an InvalidTopicException during poll() and close() sends
+     * a leave heartbeat for a group that was never created.
+     */
+    @Test
+    public void testGroupIdNotFoundExceptionWhileUnsubscribed() {
+        // Setup: member is in UNSUBSCRIBED state with epoch -1
+        when(membershipManager.state()).thenReturn(MemberState.UNSUBSCRIBED);
+        when(membershipManager.memberEpoch()).thenReturn(-1);
+
+        time.sleep(DEFAULT_HEARTBEAT_INTERVAL_MS);
+        NetworkClientDelegate.PollResult result = heartbeatRequestManager.poll(time.milliseconds());
+        assertEquals(1, result.unsentRequests.size());
+
+        // Complete the heartbeat with GROUP_ID_NOT_FOUND error
+        ClientResponse response = createHeartbeatResponse(result.unsentRequests.get(0), Errors.GROUP_ID_NOT_FOUND);
+        result.unsentRequests.get(0).handler().onComplete(response);
+
+        // Verify: no fatal error, heartbeat skipped (benign)
+        verify(membershipManager, never()).transitionToFatal();
+        verify(membershipManager).onHeartbeatRequestSkipped();
+        verify(backgroundEventHandler, never()).add(any());
+    }
+
+    /**
+     * Test that GROUP_ID_NOT_FOUND error while stable is treated as fatal.
+     * This would indicate the group was unexpectedly deleted while the member
+     * was actively participating.
+     */
+    @Test
+    public void testGroupIdNotFoundWhileStableIsFatal() {
+        // Setup: member is in STABLE state with positive epoch
+        when(membershipManager.state()).thenReturn(MemberState.STABLE);
+        when(membershipManager.memberEpoch()).thenReturn(DEFAULT_MEMBER_EPOCH);
+
+        time.sleep(DEFAULT_HEARTBEAT_INTERVAL_MS);
+        NetworkClientDelegate.PollResult result = heartbeatRequestManager.poll(time.milliseconds());
+        assertEquals(1, result.unsentRequests.size());
+
+        // Complete the heartbeat with GROUP_ID_NOT_FOUND error
+        when(coordinatorRequestManager.coordinator()).thenReturn(Optional.empty());
+        ClientResponse response = createHeartbeatResponse(result.unsentRequests.get(0), Errors.GROUP_ID_NOT_FOUND);
+        result.unsentRequests.get(0).handler().onComplete(response);
+
+        // Verify: fatal error
+        verify(membershipManager).transitionToFatal();
+        verify(backgroundEventHandler).add(any());
+    }
+
     @Test
     public void testHeartbeatResponseErrorNotifiedToGroupManagerAfterErrorPropagated() {
         time.sleep(DEFAULT_HEARTBEAT_INTERVAL_MS);
diff --git a/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ShareHeartbeatRequestManagerTest.java b/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ShareHeartbeatRequestManagerTest.java
index 8952271b250d5..20528e775deef 100644
--- a/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ShareHeartbeatRequestManagerTest.java
+++ b/clients/src/test/java/org/apache/kafka/clients/consumer/internals/ShareHeartbeatRequestManagerTest.java
@@ -354,6 +354,57 @@ public void testFailureOnFatalException() {
         verify(backgroundEventHandler).add(any());
     }
 
+    /**
+     * Test that GROUP_ID_NOT_FOUND error while unsubscribed is not treated as fatal.
+     * This can happen when the consumer never successfully joined the group
+     * (e.g., due to an InvalidTopicException during poll() and close() sends
+     * a leave heartbeat for a group that was never created.
+     */
+    @Test
+    public void testGroupIdNotFoundExceptionWhileUnsubscribed() {
+        // Setup: member is in UNSUBSCRIBED state with epoch -1
+        when(membershipManager.state()).thenReturn(MemberState.UNSUBSCRIBED);
+        when(membershipManager.memberEpoch()).thenReturn(-1);
+
+        time.sleep(DEFAULT_HEARTBEAT_INTERVAL_MS);
+        NetworkClientDelegate.PollResult result = heartbeatRequestManager.poll(time.milliseconds());
+        assertEquals(1, result.unsentRequests.size());
+
+        // Complete the heartbeat with GROUP_ID_NOT_FOUND error
+        ClientResponse response = createHeartbeatResponse(result.unsentRequests.get(0), Errors.GROUP_ID_NOT_FOUND);
+        result.unsentRequests.get(0).handler().onComplete(response);
+
+        // Verify: no fatal error, heartbeat skipped (benign)
+        verify(membershipManager, never()).transitionToFatal();
+        verify(membershipManager).onHeartbeatRequestSkipped();
+        verify(backgroundEventHandler, never()).add(any());
+    }
+
+    /**
+     * Test that GROUP_ID_NOT_FOUND error while stable is treated as fatal.
+     * This would indicate the group was unexpectedly deleted while the member
+     * was actively participating.
+     */
+    @Test
+    public void testGroupIdNotFoundWhileStableIsFatal() {
+        // Setup: member is in STABLE state with positive epoch
+        when(membershipManager.state()).thenReturn(MemberState.STABLE);
+        when(membershipManager.memberEpoch()).thenReturn(DEFAULT_MEMBER_EPOCH);
+
+        time.sleep(DEFAULT_HEARTBEAT_INTERVAL_MS);
+        NetworkClientDelegate.PollResult result = heartbeatRequestManager.poll(time.milliseconds());
+        assertEquals(1, result.unsentRequests.size());
+
+        // Complete the heartbeat with GROUP_ID_NOT_FOUND error
+        when(coordinatorRequestManager.coordinator()).thenReturn(Optional.empty());
+        ClientResponse response = createHeartbeatResponse(result.unsentRequests.get(0), Errors.GROUP_ID_NOT_FOUND);
+        result.unsentRequests.get(0).handler().onComplete(response);
+
+        // Verify: fatal error
+        verify(membershipManager).transitionToFatal();
+        verify(backgroundEventHandler).add(any());
+    }
+
     @Test
     public void testNoCoordinator() {
         when(coordinatorRequestManager.coordinator()).thenReturn(Optional.empty());