2011: two-year-old season

Dullahan was slow to show worthwhile form as a two-year-old, being well beaten in minor events at Churchill Downs in June and July. He then moved to Saratoga where he finished second in a maiden race before finishing third in the Grade II With Anticipation Stakes on turf in September. Despite having failed to win in four starts, he moved up to Grade I level for the Breeders' Futurity Stakes at Keeneland. Ridden by Kent Desormeaux he was held up in the early stages before finishing strongly to take the lead near the finish and won by three quarters of a length from Majestic City.^[2] He was badly hampered and almost fell in the early stages but recovered well, leading Desormeaux to describe him as a "super horse".^[3] In the Breeders' Cup Juvenile at Churchill Downs on 5 November, Dullahan started a 16/1 outsider and stayed on in the straight to finish fourth of the thirteen runners behind Hansen, Union Rags and Creative Cause.

2012: three-year-old season

Dullahan made his first appearance as a three-year-old at Gulfstream Park in March, where he finished second to Howe Great in the Grade III Palm Beach Stakes. A month later he was sent to Keeneland to contest the Blue Grass Stakes, in which he was matched against the Eclipse Award winner Hansen for the second time. In front of a record crowd of 40,617 Desormeaux restrained the colt in the early stages before moving him up to overtake Hansen near the finish and win going away by one and a quarter lengths.^[4] USA Today described his performance as "scintillating" and reported that Romans felt that Dullahan was by far his best chance of winning the Kentucky Derby.^[5] In the Derby, Dullahan started at odds of 12/1 in a field of twenty. He raced in the middle of the field before being switched to the outside in the straight. He made steady progress to finish third behind I'll Have Another and Bodemeister.

Dullahan skipped the Preakness to go straight for the Belmont Stakes on June 9. Following the late withdrawal of "I'll Have Another", he was made the favorite for the race,^[6] but finished fifth behind Union Rags. After a seven-week break, Dullahan returned in the Haskell Invitational Stakes at Monmouth Park in which he finished seventh, behind Paynter. A month later he was tested against older horses in the TVG Pacific Classic at Del Mar Racetrack and won by half a length from Game On Dude in a new track record time of 1:59.54. It was Dullahan's third Grade I win, all of them achieved on a synthetic surface,^[7] and gave the colt automatic entry into the Breeders' Cup Classic.^[8]

Dullahan's two remaining starts as a three-year-old were disappointing: he finished fifth when favorite for the Jamaica Handicap at Belmont in October and then ran ninth, behind Little Mike in the Breeders' Cup Turf.

2013: four-year-old season

Dullahan was sent to race in the United Arab Emirates in March 2013 but ran poorly in his two races including the Dubai World Cup in which he finished eleventh of the twelve runners behind Animal Kingdom. On his return to the USA he finished third in the Grade III Arlington Handicap but then finished eighth behind Game On Dude when he attempted to repeat his 2012 success in the Pacific Classic. Dullahan sustained a tendon injury in the Pacific Classic and was retired from racing on October 14. Six days later, the colt suffered a severe attack of colic in his stable. Despite prompt medical attention and surgery he was euthanized at 4:45 am on October 20. According to a Facebook post by Dale Romans, Dullahan was regarded my those who knew him as an incredible horse – full of personality and talent. "Love you, Dullahan – our thoughts and prayers are with you, buddy !!^[9]