Doyle begins playing rugby union at Newbridge College, County Kildare. He goes on to study veterinary science at University College Dublin, who he also represents at rugby. He makes his Ireland debut against France on January 23, 1965, scoring a try in the game. While representing Ireland he also studies at the University of Cambridge where he gains a Blue in the 1965 Varsity match against the Oxford University RFC. Doyle also studies at the University of Edinburgh and plays club rugby for Edinburgh Wanderers before returning to Ireland.
Doyle goes on to earn the distinction of never being dropped during his 20-cap international career as a flanker. Doyler, as he is affectionately known, scores the winning try against Wales in the 1967 Five Nations Championship, tours Australia with Ireland in 1967 and South Africa with the British and Irish Lions the following year.
His last game for Ireland is against Australia in October 1968, when he lines out alongside his brother Tommy. He coaches Leinster to Interprovincial Championship success five times between 1979 and 1983 before he succeeds Willie John McBride as Ireland coach during the 1984–85 season. Under In 1985, under Doyle’s stewardship, Ireland wins the Triple Crown and Five Nations Championship.
Doyle leads Ireland to the inaugural 1987 Rugby World Cup, but that joy is tinged with sadness as he suffers a heart attack at the opening dinner. He battles illness and adversity and his recovery from a brain problem is chronicled in his book 0.16.