diff --git a/lldb/include/lldb/Target/Thread.h b/lldb/include/lldb/Target/Thread.h
--- a/lldb/include/lldb/Target/Thread.h
+++ b/lldb/include/lldb/Target/Thread.h
@@ -19,6 +19,7 @@
 #include "lldb/Target/RegisterCheckpoint.h"
 #include "lldb/Target/StackFrameList.h"
 #include "lldb/Utility/Broadcaster.h"
+#include "lldb/Utility/CompletionRequest.h"
 #include "lldb/Utility/Event.h"
 #include "lldb/Utility/StructuredData.h"
 #include "lldb/Utility/UserID.h"
@@ -911,6 +912,12 @@
 
   // Thread Plan accessors:
 
+  /// Format the thread plan information for auto completion.
+  ///
+  /// \param[in] request
+  ///     The reference to the completion handler.
+  void AutoCompleteThreadPlans(CompletionRequest &request) const;
+
   /// Gets the plan which will execute next on the plan stack.
   ///
   /// \return
diff --git a/lldb/source/Commands/CommandObjectThread.cpp b/lldb/source/Commands/CommandObjectThread.cpp
--- a/lldb/source/Commands/CommandObjectThread.cpp
+++ b/lldb/source/Commands/CommandObjectThread.cpp
@@ -1985,6 +1985,15 @@
 
   ~CommandObjectThreadPlanDiscard() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    if (!m_exe_ctx.HasThreadScope() || request.GetCursorIndex())
+      return;
+
+    m_exe_ctx.GetThreadPtr()->AutoCompleteThreadPlans(request);
+  }
+
   bool DoExecute(Args &args, CommandReturnObject &result) override {
     Thread *thread = m_exe_ctx.GetThreadPtr();
     if (args.GetArgumentCount() != 1) {
diff --git a/lldb/source/Target/Thread.cpp b/lldb/source/Target/Thread.cpp
--- a/lldb/source/Target/Thread.cpp
+++ b/lldb/source/Target/Thread.cpp
@@ -1103,6 +1103,22 @@
             discarded_plan_sp->GetThread().GetID());
 }
 
+void Thread::AutoCompleteThreadPlans(CompletionRequest &request) const {
+  const ThreadPlanStack &plans = GetPlans();
+  if (!plans.AnyPlans())
+    return;
+
+  // Iterate from the second plan (index: 1) to skip the base plan.
+  ThreadPlanSP p;
+  uint32_t i = 1;
+  while (p = plans.GetPlanByIndex(i, false)) {
+    StreamString strm;
+    p->GetDescription(&strm, eDescriptionLevelInitial);
+    request.TryCompleteCurrentArg(std::to_string(i), strm.GetString());
+    i++;
+  }
+}
+
 ThreadPlan *Thread::GetCurrentPlan() const {
   return GetPlans().GetCurrentPlan().get();
 }
diff --git a/lldb/test/API/functionalities/completion/TestCompletion.py b/lldb/test/API/functionalities/completion/TestCompletion.py
--- a/lldb/test/API/functionalities/completion/TestCompletion.py
+++ b/lldb/test/API/functionalities/completion/TestCompletion.py
@@ -329,6 +329,19 @@
                               ['target.process.thread.step-avoid-regexp',
                                'target.process.thread.trace-thread'])
 
+    def test_thread_plan_discard(self):
+        self.build()
+        (_, _, thread, _) = lldbutil.run_to_source_breakpoint(self,
+                                          'ptr_foo', lldb.SBFileSpec("main.cpp"))
+        self.assertTrue(thread)
+        self.complete_from_to('thread plan discard ', 'thread plan discard ')
+
+        source_path = os.path.join(self.getSourceDir(), "thread_plan_script.py")
+        self.runCmd("command script import '%s'"%(source_path))
+        self.runCmd("thread step-scripted -C thread_plan_script.PushPlanStack")
+        self.complete_from_to('thread plan discard ', 'thread plan discard 1')
+        self.runCmd('thread plan discard 1')
+
     def test_target_space(self):
         """Test that 'target ' completes to ['create', 'delete', 'list',
         'modules', 'select', 'stop-hook', 'variable']."""
diff --git a/lldb/test/API/functionalities/completion/thread_plan_script.py b/lldb/test/API/functionalities/completion/thread_plan_script.py
new file mode 100644
--- /dev/null
+++ b/lldb/test/API/functionalities/completion/thread_plan_script.py
@@ -0,0 +1,20 @@
+#############################################################################
+# This script is just to provide a thread plan which won't be popped instantly
+# for the completion test. The thread plan class below won't really do anything
+# itself.
+
+import lldb
+
+class PushPlanStack:
+
+    def __init__(self, thread_plan, dict):
+        pass
+
+    def explains_stop(self, event):
+        return False
+
+    def should_stop(self, event):
+        return True
+
+    def should_step(self):
+        return True