Program hangs/Issue with WaitForSingleObject/CreateProcess in Delphi

Don't assign your hRead handle to the child process's hStdInput. You are not sending any data to the child process. Don't let the child process inherit your hRead handle at all. Use SetHandleInformation() to remove the HANDLE_FLAG_INHERIT flag from it.

And, you need to close your hWrite handle after the child process has inherited it, otherwise the pipe will remain open after the child process has terminated. You are not writing anything to the child process, so you don't need to leave your original hWrite handle open. When the child process terminates, its inherited hWrite handle will be closed, thus breaking the pipe, allowing ReadFile() to stop waiting for further data.

See How to read output from cmd.exe using CreateProcess() and CreatePipe() for more details about the use of pipe handles during I/O redirection.

Then, you can remove the outer repeat loop altogether. Just loop on ReadFile() until it fails, then call WaitForSingleObject() on the hProcess handle before cleaning up.

And just an FYI, using AMemo.Lines.Text := AMemo.Lines.Text + String(pBuffer); is a very inefficient way to append strings to a TMemo, especially over a long time.

Try something more like this instead:

procedure Tform_Main.CaptureConsoleOutput(const ACommand, AParameters: String; AMemo: TMemo);
const
  CReadBuffer = 65536;
var
  saSecurity: TSecurityAttributes;
  hRead:      THandle;
  hWrite:     THandle;
  suiStartup: TStartupInfo;
  piProcess:  TProcessInformation;
  pBuffer:    array[0..CReadBuffer] of AnsiChar;
  dRead:      DWord;
begin
  (*
   ACommand:      ex. {GoGetter.exe}
   AParameters:   ex. {C:\temp\downloads\ c:\temp\urls.txt 1}
  *)
  saSecurity.nLength              := SizeOf(TSecurityAttributes);
  saSecurity.bInheritHandle       := True;
  saSecurity.lpSecurityDescriptor := nil;

  if CreatePipe(hRead, hWrite, @saSecurity, 0) then
  try
    SetHandleInformation(hRead, HANDLE_FLAG_INHERIT, 0);

    ZeroMemory(@suiStartup, SizeOf(suiStartup));
    suiStartup.cb          := SizeOf(TStartupInfo);
    suiStartup.hStdInput   := GetStdHandle(STD_INPUT_HANDLE);
    suiStartup.hStdOutput  := hWrite;
    suiStartup.hStdError   := hWrite;
    suiStartup.dwFlags     := STARTF_USESTDHANDLES;

    Screen.Cursor := crHourglass;
    Application.ProcessMessages;

    try
      if CreateProcess(nil, PChar(ACommand + ' ' + AParameters), @saSecurity, @saSecurity, True, CREATE_NO_WINDOW or NORMAL_PRIORITY_CLASS,
                       nil, nil, suiStartup, piProcess) then
      try
        CloseHandle(piProcess.hThread);

        CloseHandle(hWrite);
        hWrite := INVALID_HANDLE_VALUE;

        repeat
          Application.ProcessMessages();
          if (not ReadFile(hRead, pBuffer[0], CReadBuffer, dRead, nil)) or (dRead = 0) then
            Break;
          pBuffer[dRead] := #0;
          OemToAnsi(pBuffer, pBuffer);
          AMemo.SelStart := AMemo.GetTextLen();
          AMemo.SelLength := 0;
          AMemo.SelText := String(pBuffer);
          SendMessage(AMemo.Handle, WM_VSCROLL, SB_BOTTOM, 0);
        until False;

        WaitForSingleObject(piProcess.hProcess, INFINITE);
      finally
        CloseHandle(piProcess.hProcess);
      end;
    finally
      Done();
    end;
  finally
    CloseHandle(hRead);
    if hWrite <> INVALID_HANDLE_VALUE then
      CloseHandle(hWrite);
  end;
end;

Then, consider moving this code into a separate worker thread so you don't block your main UI thread anymore. Then you won't need ProcessMessages() anymore. Otherwise, if you really want to call ProcessMessages() inside the loop, use a named pipe instead of an anonymous pipe, then you can read asynchronously using OVERLAPPED I/O (see Overlapped I/O on anonymous pipe).