Besides assistant manager roles at Bolton, Blackburn and West Ham, McDonald has also managed Carlisle United and Blackpool.
"I’m pleased to welcome Neil to the Club and look forward to working with him," Hull City head coach Mike Phelan told the club's official website.
"It was important that we added to the backroom staff here and Neil brings a wealth of football experience which will be of huge importance as the season progresses".
Hull had been without an assistant manager since Stephen Clemence joined Aston Villa to team up with former Hull boss Steve Bruce.