McQuillan turned professional, and finished 7th at the 2003 Spring qualifying tournament for the
Canadian Tour. His most successful Canadian Tour result to date has been a victory at the 2005 Telus Edmonton Open, scoring 13-under-par 271 at the Edmonton Golf & Country Club, from 30 June to 3 July; McQuillan edged the runner-up, promising amateur
Graham DeLaet, and won $24,000 (Canadian funds). McQuillan played in three
Nationwide Tour events in 2005, with his best finish a tie for 25th position in the Alberta Classic. He finished runner-up at the 2006
Canadian Tour Championship. For a time in the mid-2000s, he represented the
Cataraqui Golf and Country Club in Kingston, but no longer does so. However, he still works with Dickey, now a teacher at Cataraqui. McQuillan received an honorary membership from Cataraqui on 21 December 2010, after he earned PGA Tour playing privileges for 2011. McQuillan successfully played on the Tar Heels Tour in the Carolinas during the spring of 2008, in preparation for a return to
PGA Tour qualifying in the fall of 2008. He set a new competitive course record at Cataraqui in mid-July 2008, winning the Cataraqui Pro-Am tournament, with a score of 62, 8-under-par, breaking the previous mark by one stroke. McQuillan played on the
EGolf Professional Tour with success early in 2010, and played well at the
Seaforth Country Classic on the Canadian Tour in August 2010, finishing in 4th place. He retains exempt status on the Canadian Tour for 2011. McQuillan worked as a
bartender in Kingston to supplement his income between stints on pro golf tours.
PGA Tour McQuillan entered
PGA Tour qualifying in the fall of 2010, beginning at first stage. He scored 67 in the final round at first stage to advance. He then advanced to the third and final stage of 2010
PGA Tour qualifying, by placing third at the second stage qualifying event, hosted by the Bear Creek Golf Club in
Murrieta, California. McQuillan successfully gained PGA Tour status for the 2011 season, by finishing T16 at 11-under-par after six rounds, at final stage, hosted by the Orange County National facility near
Orlando, Florida. This was his first trip to the finals. McQuillan made his 2011 debut at the
Sony Open in Hawaii in
Honolulu, the first PGA Tour event of his career. He survived the 36-hole cut with rounds of 68–69, then finishing on the 36-hole final day (caused by a rainout on the scheduled first round day) with 71-74 for 282 and 55th place, winning $12,705. McQuillan earned last-minute entry to the
Bob Hope Classic in
Palm Springs, shot a first-round 7-under-par 65 which included seven birdies and an eagle, but followed up with rounds of 76-73-77 to miss the fourth-round cut with a score of 3-over-par 291. At the
Farmers Insurance Open in
San Diego, McQuillan struggled with rounds of 74–77 to miss the halfway cut with a score of 7-over-par 151. McQuillan scored 76-76-68 for 6-over-par 220 in the
AT&T National Pro-Am, missing the 54-hole cut. McQuillan shot rounds of 76–73 at the
Mayakoba Golf Classic near
Cancun, Mexico, missing the 36-hole cut. McQuillan scored 71–74 at the 2011
Puerto Rico Open, held just east of
San Juan, Puerto Rico, to miss the 36-hole cut by one stroke. After playing on the PGA Tour for ten weeks in 2011, making just one cut in six events, McQuillan said the course setups he had been facing were much tougher than anything he had seen before, but added that he was settling into life on the Tour, and anticipated an improvement in his performance as he gained experience. McQuillan dropped down to the Nationwide Tour for his next event, the Louisiana Classic. After opening with 70–66 to move into contention, he struggled on the weekend with rounds of 76 and 73 to finish at one-over-par 285, tied for 62nd place, earning $1,463. McQuillan's struggles continued at the
Valero Texas Open, where he missed the 36-hole cut after rounds of 82–75. McQuillan shot 78–77 at the
Zurich Classic of New Orleans to miss the cut by 12 strokes. McQuillan played the Nationwide Tour's Stadion Classic at UGA on his former home course in
Athens, Georgia, but missed the 36-hole cut by three strokes with scores of 71–76. His next event was the
HP Byron Nelson Championship near
Dallas, where his scores of 73-73 missed the 36-hole cut by three strokes. McQuillan played the Nationwide Tour's
Maryland event, the
Melwood Prince George's County Open, and missed the cut by two shots with scores of 72–71. He shot 70–73 to miss the 36-hole cut by one stroke at the FedEx St. Jude Classic near
Memphis. Although he missed another cut, by four strokes, at the Travelers Championship near
Hartford with scores of 73–67, his second round was his first under 70 on the PGA Tour since Pebble Beach, four months before. McQuillan broke out of his slump at the
John Deere Classic, in
Silvis, Illinois. He opened with 64 to tie for second place, one stroke out of the lead. He made the halfway cut comfortably with a second-round 69, then played well on the weekend with rounds of 70–64, finishing with 17-under-par 267, to tie for third place, winning $261,000. His three eagles led the field. His position on the
Official World Golf Ranking jumped to #506. McQuillan continued his good play at the
Viking Classic, near
Jackson, Mississippi, where he scored 72-65-71-67, for 13-under-par 275, to tie for 34th place, winning $18,990. McQuillan made his third straight cut at the
RBC Canadian Open, held over the
Shaughnessy Golf & Country Club in Vancouver, scoring 68-73-74-70 for 5-over-par 285, tied for 31st place, and winning $33,800. McQuillan saw his streak of three straight made cuts end at the 2011
Greenbrier Classic, where his scores of 71-74 missed the 36-hole cut by four strokes. McQuillan tied for sixth place at the 2011 Reno-Tahoe Open with scores of 71-69-71-66 for a 277 total, 11-under-par, winning $97,125. McQuillan's scores of 69–70 at the
Wyndham Championship missed the halfway cut by two strokes, and he failed to make the top 125-point scorers for the FedEx Cup, missing the four playoff events. McQuillan made seven cuts in 21 events and ended the season 137th on the money list. In 2017, McQuillan qualified for the
PGA Tour Canada. ==Professional wins (2)==