diff --git a/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/execution/ExecuteThreadRunner.scala b/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/execution/ExecuteThreadRunner.scala
index b7c335c6cfcfe..9f606b698d30c 100644
--- a/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/execution/ExecuteThreadRunner.scala
+++ b/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/execution/ExecuteThreadRunner.scala
@@ -193,6 +193,11 @@ private[connect] class ExecuteThreadRunner(executeHolder: ExecuteHolder) extends
       return
     }
 
+    // SPARK-53339: Post the Started event here, right after the CAS succeeds, to ensure that
+    // postStarted() is never called when interrupt() has already transitioned the state to
+    // interrupted. This eliminates the race between postStarted() and interrupt().
+    executeHolder.eventsManager.postStarted()
+
     // `withSession` ensures that session-specific artifacts (such as JARs and class files) are
     // available during processing.
     executeHolder.sessionHolder.withSession { session =>
diff --git a/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/ExecuteEventsManager.scala b/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/ExecuteEventsManager.scala
index fcf01d5d29ab3..286163e135d2a 100644
--- a/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/ExecuteEventsManager.scala
+++ b/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/ExecuteEventsManager.scala
@@ -188,9 +188,7 @@ case class ExecuteEventsManager(executeHolder: ExecuteHolder, clock: Clock) {
       request.getPlan.getOpTypeCase match {
         case proto.Plan.OpTypeCase.COMMAND => request.getPlan.getCommand
         case proto.Plan.OpTypeCase.ROOT => request.getPlan.getRoot
-        case _ =>
-          throw new UnsupportedOperationException(
-            s"${request.getPlan.getOpTypeCase} not supported.")
+        case _ => request.getPlan
       }
 
     val event = SparkListenerConnectOperationStarted(
@@ -248,8 +246,11 @@ case class ExecuteEventsManager(executeHolder: ExecuteHolder, clock: Clock) {
    * Post @link org.apache.spark.sql.connect.service.SparkListenerConnectOperationCanceled.
    */
   def postCanceled(): Unit = {
+    // SPARK-53339: Pending is included to handle the case where interrupt() is called before
+    // postStarted() transitions the status from Pending to Started.
     assertStatus(
       List(
+        ExecuteStatus.Pending,
         ExecuteStatus.Started,
         ExecuteStatus.Analyzed,
         ExecuteStatus.ReadyForExecution,
@@ -269,8 +270,11 @@ case class ExecuteEventsManager(executeHolder: ExecuteHolder, clock: Clock) {
    *   The message of the error thrown during the request.
    */
   def postFailed(errorMessage: String): Unit = {
+    // SPARK-53339: Pending is included to handle the case where postStarted() itself throws
+    // an exception (e.g., session state check failure) before transitioning from Pending.
     assertStatus(
       List(
+        ExecuteStatus.Pending,
         ExecuteStatus.Started,
         ExecuteStatus.Analyzed,
         ExecuteStatus.ReadyForExecution,
diff --git a/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/SparkConnectExecutionManager.scala b/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/SparkConnectExecutionManager.scala
index bb51438ce90f6..2a936b526d96a 100644
--- a/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/SparkConnectExecutionManager.scala
+++ b/sql/connect/server/src/main/scala/org/apache/spark/sql/connect/service/SparkConnectExecutionManager.scala
@@ -35,6 +35,7 @@ import org.apache.spark.sql.catalyst.util.DateTimeConstants.NANOS_PER_MILLIS
 import org.apache.spark.sql.connect.IllegalStateErrors
 import org.apache.spark.sql.connect.config.Connect.{CONNECT_EXECUTE_MANAGER_ABANDONED_TOMBSTONES_SIZE, CONNECT_EXECUTE_MANAGER_DETACHED_TIMEOUT, CONNECT_EXECUTE_MANAGER_MAINTENANCE_INTERVAL}
 import org.apache.spark.sql.connect.execution.ExecuteGrpcResponseSender
+import org.apache.spark.sql.connect.planner.InvalidInputErrors
 import org.apache.spark.util.ThreadUtils
 
 // Unique key identifying execution by combination of user, session and operation id
@@ -191,7 +192,16 @@ private[connect] class SparkConnectExecutionManager() extends Logging {
       responseObserver: StreamObserver[proto.ExecutePlanResponse]): ExecuteHolder = {
     val executeHolder = createExecuteHolder(executeKey, request, sessionHolder)
     try {
-      executeHolder.eventsManager.postStarted()
+      // SPARK-53339: Validate the plan before starting the execution thread.
+      // postStarted() was moved into executeInternal(), so invalid plans that previously
+      // caused postStarted() to throw (and thus triggered removeExecuteHolder in this
+      // catch block) now fail asynchronously inside the execution thread. This early
+      // validation ensures that invalid plans are still caught synchronously here.
+      request.getPlan.getOpTypeCase match {
+        case proto.Plan.OpTypeCase.ROOT | proto.Plan.OpTypeCase.COMMAND => // valid
+        case other =>
+          throw InvalidInputErrors.invalidOneOfField(other, request.getPlan.getDescriptorForType)
+      }
       executeHolder.start()
     } catch {
       // Errors raised before the execution holder has finished spawning a thread are considered
diff --git a/sql/connect/server/src/test/scala/org/apache/spark/sql/connect/service/ExecuteEventsManagerSuite.scala b/sql/connect/server/src/test/scala/org/apache/spark/sql/connect/service/ExecuteEventsManagerSuite.scala
index a96d0ab977c5c..f5349a48330c3 100644
--- a/sql/connect/server/src/test/scala/org/apache/spark/sql/connect/service/ExecuteEventsManagerSuite.scala
+++ b/sql/connect/server/src/test/scala/org/apache/spark/sql/connect/service/ExecuteEventsManagerSuite.scala
@@ -138,6 +138,36 @@ class ExecuteEventsManagerSuite
         .isInstanceOf[SparkListenerConnectOperationCanceled])
   }
 
+  test("SPARK-53339: post canceled from Pending state") {
+    val events = setupEvents(ExecuteStatus.Pending)
+    events.postCanceled()
+    assert(events.status == ExecuteStatus.Canceled)
+    assert(events.terminationReason.contains(TerminationReason.Canceled))
+  }
+
+  test("SPARK-53339: post failed from Pending state") {
+    val events = setupEvents(ExecuteStatus.Pending)
+    events.postFailed(DEFAULT_ERROR)
+    assert(events.status == ExecuteStatus.Failed)
+    assert(events.terminationReason.contains(TerminationReason.Failed))
+  }
+
+  test("SPARK-53339: Pending to Canceled to Closed transition") {
+    val events = setupEvents(ExecuteStatus.Pending)
+    events.postCanceled()
+    events.postClosed()
+    assert(events.status == ExecuteStatus.Closed)
+    assert(events.terminationReason.contains(TerminationReason.Canceled))
+  }
+
+  test("SPARK-53339: Pending to Failed to Closed transition") {
+    val events = setupEvents(ExecuteStatus.Pending)
+    events.postFailed(DEFAULT_ERROR)
+    events.postClosed()
+    assert(events.status == ExecuteStatus.Closed)
+    assert(events.terminationReason.contains(TerminationReason.Failed))
+  }
+
   test("SPARK-43923: post failed") {
     val events = setupEvents(ExecuteStatus.Started)
     events.postFailed(DEFAULT_ERROR)