type
  TMySpecialthread = class(TThread)
  Begin
   {...}
  protected
      procedure Execute; override;
   {...}    
  end;
  
Var
  EventHandle: THandle;
  ThreadHandle: THandle;
  MySpecialthread: TMySpecialthread;
  
procedure ToDoAfterMySpecialThreadHasFinished; stdcall;
Var ObjRtn: Cardinal;
begin
  ObjRtn := WaitForSingleObject(EventHandle, INFINITE);
  MySpecialThread.Terminate;
  Showmessage('MySpecialThread is Ready'); // eben nur als Beispiel
  { ..  DoToListe abarbeiten,
    was nach Ende des MySpecialThread zu erledigen ist ... }
  ExitThread(0);
end;

procedure MySpecialthread.Execute;
begin
   {... do it  .....}
  SetEvent(EventHandle);
end;
  
procedure TForm1.FormCreate(Sender: TObject);
var
  ThreadID: Cardinal;
begin
  EventHandle := CreateEvent(Nil, True, False, 'MySpecialThreadEvent');
  ThreadHandle := CreateThread(nil, 0, @ToDoAfterMySpecialThreadHasFinished, nil, 0, ThreadId);
  MySpecialThread:=TMySpecialThread.create(false);
  MySpecialThread.FreeOnTerminate:=false; // oder nach Bedarf true
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Button1.Enabled:=false;
  MySpecialThread.Resume;
end;