Moriarty was a lightly built full-forward — despite standing only 5'10" (178 cm), and weighing approximately 60 kg, he had the ability to jump over opponents and take strong over-head marks — who became a spectacular success after leaving Essendon Football Club at the end of 1923 and crossing to Fitzroy Football Club.

Moriarty transferred to the Essendon VFL club in 1922, playing thirteen games at full-forward, including the Semi-final, against Carlton, on 23 September 1922.

He was controversially dropped from the team for the Preliminary Final, against Fitzroy, on 7 October 1922, and half-back flanker Greg Stockdale moved to full-forward in his place.

Based upon that performance, Stockdale became the team's full-forward in 1923 — Stockdale scored 68 goals in the 1923 season breaking the VFL's (then) record of 66 goals set jointly by Fitzroy's Jimmy Freake and Collingwood's Dick Lee in 1915, and Moriarty was unable to break back into the senior team.

He topped Fitzroy's goal kicking list every year between 1924 and 1933, except for 1930, and was voted the club's best and fairest player in 1927 during an era when an award of this type was not made every season.