During his stint with Connacht, Fanning made eight appearances, playing in the league and the Challenge Cup. He was also part of the Connacht team to play against . Fanning returned to his club St Mary's College, where he was named as captain for the 2013–14 season before being called up to the Leinster senior squad. He made his senior debut for Leinster on 9 September 2013 against the Welsh side Scarlets in the 2013–14 Pro12.