He played for Mervue United's under 19 side for the 2011–12 season, making 2 appearances for the first team in the League of Ireland First Division.
He won the 2015 League of Ireland Cup for the club, by saving 2 penalties against Galway United in the final.
[4] He played in the 2016 League of Ireland Cup Final also, as Pat's won 4–1 against Limerick to retain the title.
[6] On 7 August 2017, O'Malley joined his old Pat's teammate Chris Forrester at League 1 side Peterborough United for an undisclosed fee expected to be in the region of €100,000, and made his debut in a 2–0 victory against Southampton Under-21s in the EFL Trophy.
[8] In April 2020, he had announced that he would be retiring from football upon the conclusion of his contract in order to return home and begin working in the financial sector.