Racing at age three, Ballymoss began by running unplaced in the seven-furlong Madrid Handicap at the Curragh but then won the Trigo Stakes at Leopardstown over one and a half miles.
[2] In the build-up to the Derby, Ballymoss incurred a minor injury, leading McShain to cancel his plans to travel to England for the race.
At York in August, Ballymoss started odds-on favourite for the Great Voltigeur Stakes but finished well beaten behind Brioche.
He was backed down from 11/4 to 7/4 favourite on the day of the race and took the lead a furlong and a half from the finish, pulling clear to win by three lengths from Almeria.
On his final appearance, he was shipped to Laurel Park Racecourse in the United States for the Washington, D.C. International, which also attracted entries from Germany, the Soviet Union, Venezuela, and Argentina.
He finished third, beaten three and a half lengths by Tudor Era and losing second place by a head to the Australian champion Sailor's Guide.
[7] When Ballymoss was retired at the end of the 1958 racing season, his earnings of £114,150 were a record for a horse trained in Britain or Ireland, surpassing the mark of £76,577 set by Tulyar in 1952.
Notably, he sired Royal Palace, winner of the 1967 Epsom Derby and 2,000 Guineas, plus Ballymoss Nisei (バリモスニセイ) who won in Japan and where he stood at stud.