‘Fergus’, born in Dublin, played senior rugby for University College Dublin, before beginning his International career in 1970. He captained Ireland 18 times during his 61 caps and scored 3 tries. In 1971 he was selected to tour with the British Lions to Australia and New Zealand. He contested with John Taylor for the test place and was finally given the nod ahead of Taylor for the third test. Unfortunately a sore throat on the morning of the game meant that he had to withdraw and he was then unable to regain the place from Taylor for the final test.

Another player with long golden shanks, Slattery' distinctive appearance and marauding loose forward play labeled him as another player to watch for the future – excepting that an unsuspecting punch against Canterbury left him with an ugly mouth injury that required a plate for the majority of the tour. Slattery toured again in 1974 playing in all four tests and captaining the side for 2 provincial matches.