Treacy left Drogheda United to sign for another Premier Division side, St Patrick's Athletic on a one-year contract. He made his debut for the club, coming on as a 53rd minute substitute, in a 1–0 win against Longford Town on 11 March 2016. Treacy played 14 league games for the Saints through the season, scoring one goal away to Derry City. He featured in all 4 games in the club's UEFA Europa League campaign and once set up a goal for the Saints in a 2–1 loss against Jeunesse Esch in the second leg of the UEFA Europa League first qualifying round. However due to injuries, Treacy was not in the squad for the League Cup Final as Pats beat Limerick 4–1 to retain the trophy. At the end of the 2016 season, he went on to make eighteen appearances and scoring once for the club. Following this, St Patrick's Athletic released Treacy upon expiry of his contract.