O'Hanlon excelled at underage level playing at left back and in May 2011, at the age of 15, he was snapped up by Premier League club Liverpool, despite interest from Premier League rivals Manchester United, Arsenal, Chelsea, as well as Spanish giants Real Madrid, with comparisons in playing style being made with Wales international Gareth Bale.
[6] O'Hanlon returned home to Dublin and signed for League of Ireland Premier Division side St Patrick's Athletic on 9 January 2017 on a 2-year contract ahead of the 2017 season, alongside Barry Murphy and Kurtis Byrne.
[7][8][9][10][11] On 31 January 2017 O'Hanlon made his Pats debut away to Bray Wanderers in the Leinster Senior Cup, scoring the fourth goal in a 4–0 win for the Saints at the Carlisle Grounds.
[12][13] He began the season alternating between left wing and attacking midfield roles, impressing Pats supporters and media in the Dublin derby wins over Shamrock Rovers[14] and Bohemians.
He scored his third goal of the season against Firhouse Clover amongst an experimental lineup in a 2–1 Leinster Senior Cup Quarter-final win, looping a shot over the goalkeeper from 25 yards.
He appeared in their 2021 FAI Cup campaign, setting up an extra-time winner for Alan Byrne in a 2–1 win over Ulster Senior League side Cockhill Celtic in the Qualifying Round on 10 July 2021.