MacDonald made his UFC debut on October 10, 2006, at Ortiz vs. Shamrock 3: The Final Chapter against the favored The Ultimate Fighter 3 finalist Ed Herman. In an upset, MacDonald won the bout via triangle choke in the first round. MacDonald followed up the performance with a win over The Ultimate Fighter 1 veteran Chris Leben via modified guillotine choke in the second round. Both victories earned Submission of the Night honors.
At the MFC 21 event on May 15, 2009, MacDonald announced that he was returning to the Canadian promotion Maximum Fighting Championship. He fought Travis Lutter in the main event of MFC 22 on October 2, 2009, losing a unanimous decision.
MacDonald was scheduled to face Rafael Natal on December 11, 2010, at UFC 124, but pulled out of the fight after suffering an injury in training.
MacDonald faced Alan Belcher on September 17, 2011 at UFC Fight Night 25, losing via Verbal submission due to strikes in the first round.
MacDonald faced Tom Lawlor on May 15, 2012 at UFC on Fuel TV: Korean Zombie vs. Poirier. He lost the fight via KO in the first round. On February 28, 2013, MacDonald announced his retirement from MMA, leaving his UFC record standing at 6-8.
