[3] Mac Swiney's dam Halla Na Saoire was an unraced sister to the Derrinstown Stud Derby Trial winner Light Heavy.

In the following month, he started at odds of 15/2 for a maiden over the same course and distance and recorded his first success as he overtook the Aidan O'Brien-trained favourite Wembley inside the final furlongs and pulled clear to win by one and a half lengths.

[5] On 6 August, the colt was stepped up in class to contest the Group 3 Tyros Stakes at Leopardstown Racecourse but made little impact as he faded from contention in the last quarter mile and came home ninth of the ten runners behind Military Style.

Despite his poor run at Leopardstown, Mac Swiney was moved up in class again to contest the Group 2 Futurity Stakes over seven furlong on soft ground at the Curragh sixteen days later.

"[7] Mac Swiney was elevated to the highest class for the Group 1 National Stakes at the Curragh on 13 September but never looked likely to win and came home eighth, beaten just over eight lengths by the winner Thunder Moon.

In a race run in heavy rain Mac Swiney led from the start and held off a sustained challenge from his stablemate Poetic Flare to win by a short head with a gap of 3+1⁄2 lengths back to Van Gogh in third.

[13] In the Irish Derby at the Curragh three weeks later he was disappointing, reaching second place in the straight before fading in the last quarter mile to finish sixth of the eleven runners behind Hurricane Lane.

[14] At York Racecourse in August the colt was matched against older horses in the International Stakes over 10+1⁄2 furlongs but after leading for most of the race he was overtaken early in the straight and came home fifth behind the four-year-old Mishriff, beaten more than eight lengths by the winner.

On 11 September at Leopardstown Mac Swiney was dropped in class and distance for the Group 2 Clipper Boomerang Mile in which he started 7/2 favourite but faded badly in the closing stages and finished unplaced.