That completes the team that will face the United States at Oakland Hills Country Club in suburban Detroit next month.
Montgomerie has struggled this year and fought through a public and very difficult divorce. He has a record of 10-2-3 in his last three Ryder Cup appearances and has played in the event six times overall with a mark of 16-6-5.
His third place finish Sunday at the BMW International Open left him at No. 16 on the European Points List.
"Bernhard knows what I can do because he's played with me and he felt that I could help his team," Montgomerie said. "It has been a tough time for me recently and so this news is great news for me personally."
"To play in the Ryder Cup is a dream," said Donald, a tour rookie.