 Holmes, a left-back, began his career with St. John Bosco.He joined Coventry City as apprentice and was a member of the FA Youth Cup Final side in 1970.He turned professional in November 1970 and became the Republic of Ireland's youngest ever full international at 17 years, 200 days when he came on as a 74th-minute substitute for Don Givens in the 4–1 defeat in the European Championship Qualifier against Austria at Dalymount Park on 30 May 1971.