Index: lldb/include/lldb/Interpreter/CommandCompletions.h
===================================================================
--- lldb/include/lldb/Interpreter/CommandCompletions.h
+++ lldb/include/lldb/Interpreter/CommandCompletions.h
@@ -40,10 +40,11 @@
     eProcessPluginCompletion = (1u << 12),
     eProcessIDCompletion = (1u << 13),
     eFrameIndexCompletion = (1u << 14),
+    eThreadIndexCompletion = (1u << 15),
     // This item serves two purposes.  It is the last element in the enum, so
     // you can add custom enums starting from here in your Option class. Also
     // if you & in this bit the base code will not process the option.
-    eCustomCompletion = (1u << 15)
+    eCustomCompletion = (1u << 16)
   };
 
   static bool InvokeCommonCompletionCallbacks(
@@ -107,6 +108,9 @@
 
   static void FrameIndex(CommandInterpreter &interpreter,
                          CompletionRequest &request, SearchFilter *searcher);
+
+  static void ThreadIndex(CommandInterpreter &interpreter,
+                          CompletionRequest &request, SearchFilter *searcher);
 };
 
 } // namespace lldb_private
Index: lldb/source/Commands/CommandCompletions.cpp
===================================================================
--- lldb/source/Commands/CommandCompletions.cpp
+++ lldb/source/Commands/CommandCompletions.cpp
@@ -18,6 +18,7 @@
 #include "lldb/Interpreter/OptionValueProperties.h"
 #include "lldb/Symbol/CompileUnit.h"
 #include "lldb/Symbol/Variable.h"
+#include "lldb/Target/Process.h"
 #include "lldb/Target/RegisterContext.h"
 #include "lldb/Target/Thread.h"
 #include "lldb/Utility/FileSpec.h"
@@ -63,6 +64,7 @@
       {eProcessPluginCompletion, CommandCompletions::ProcessPluginNames},
       {eProcessIDCompletion, CommandCompletions::ProcessIDs},
       {eFrameIndexCompletion, CommandCompletions::FrameIndex},
+      {eThreadIndexCompletion, CommandCompletions::ThreadIndex},
       {eNoCompletion, nullptr} // This one has to be last in the list.
   };
 
@@ -649,4 +651,21 @@
     frame_sp->Dump(&strm, false, true);
     request.TryCompleteCurrentArg(std::to_string(i), strm.GetString());
   }
-}
\ No newline at end of file
+}
+
+void CommandCompletions::ThreadIndex(CommandInterpreter &interpreter,
+                                     CompletionRequest &request,
+                                     SearchFilter *searcher) {
+  const ExecutionContext &exe_ctx = interpreter.GetExecutionContext();
+  if (!exe_ctx.HasProcessScope())
+    return;
+
+  ThreadList &threads = exe_ctx.GetProcessPtr()->GetThreadList();
+  lldb::ThreadSP thread_sp;
+  for (uint32_t idx = 0; thread_sp = threads.GetThreadAtIndex(idx); ++idx) {
+    StreamString strm;
+    thread_sp->GetStatus(strm, 0, 1, 1, true);
+    request.TryCompleteCurrentArg(std::to_string(thread_sp->GetIndexID()),
+                                  strm.GetString());
+  }
+}
Index: lldb/source/Commands/CommandObjectThread.cpp
===================================================================
--- lldb/source/Commands/CommandObjectThread.cpp
+++ lldb/source/Commands/CommandObjectThread.cpp
@@ -541,6 +541,17 @@
 
   ~CommandObjectThreadStepWithTypeAndScope() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    if (request.GetCursorIndex())
+      return;
+
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), CommandCompletions::eThreadIndexCompletion,
+        request, nullptr);
+  }
+
   Options *GetOptions() override { return &m_all_options; }
 
 protected:
@@ -808,6 +819,14 @@
 
   ~CommandObjectThreadContinue() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), CommandCompletions::eThreadIndexCompletion,
+        request, nullptr);
+  }
+
   bool DoExecute(Args &command, CommandReturnObject &result) override {
     bool synchronous_execution = m_interpreter.GetSynchronous();
 
@@ -1300,6 +1319,17 @@
 
   ~CommandObjectThreadSelect() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    if (request.GetCursorIndex())
+      return;
+
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), CommandCompletions::eThreadIndexCompletion,
+        request, nullptr);
+  }
+
 protected:
   bool DoExecute(Args &command, CommandReturnObject &result) override {
     Process *process = m_exe_ctx.GetProcessPtr();
@@ -1431,6 +1461,14 @@
 
   ~CommandObjectThreadInfo() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), CommandCompletions::eThreadIndexCompletion,
+        request, nullptr);
+  }
+
   Options *GetOptions() override { return &m_options; }
 
   bool HandleOneThread(lldb::tid_t tid, CommandReturnObject &result) override {
@@ -1475,6 +1513,14 @@
 
   ~CommandObjectThreadException() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), CommandCompletions::eThreadIndexCompletion,
+        request, nullptr);
+  }
+
   bool HandleOneThread(lldb::tid_t tid, CommandReturnObject &result) override {
     ThreadSP thread_sp =
         m_exe_ctx.GetProcessPtr()->GetThreadList().FindThreadByID(tid);
Index: lldb/test/API/functionalities/completion/TestCompletion.py
===================================================================
--- lldb/test/API/functionalities/completion/TestCompletion.py
+++ lldb/test/API/functionalities/completion/TestCompletion.py
@@ -363,6 +363,22 @@
         """Test that 'target va' completes to 'target variable '."""
         self.complete_from_to('target va', 'target variable ')
 
+    def test_common_completion_thread_index(self):
+        subcommands = ['continue', 'info', 'exception', 'select',
+                       'step-in', 'step-inst', 'step-inst-over', 'step-out', 'step-over', 'step-script']
+
+        # Completion should not work without threads.
+        for subcommand in subcommands:
+            self.complete_from_to('thread ' + subcommand + ' ',
+                                  'thread ' + subcommand + ' ')
+
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, '// Break here', lldb.SBFileSpec("main.cpp"))
+
+        # At least we have the thread at the index of 1 now.
+        for subcommand in subcommands:
+            self.complete_from_to('thread ' + subcommand + ' ', ['1'])
+
     def test_command_argument_completion(self):
         """Test completion of command arguments"""
         self.complete_from_to("watchpoint set variable -", ["-w", "-s"])