Born in Dublin, Ireland, Rooney came through the youth setup at St Patrick's Athletic. He was a part of the team that won the national under-19 league in 2015 by beating Derry City 3–2 in the final in Buncrana.

His debut in senior football was on 22 September 2015, a 1–0 loss against Dundalk in the semi-final of the Leinster Senior Cup at Richmond Park. Rooney went on to be an unused substitute in another 9 games for Pats in the 2015 season. He signed for Dublin rivals Bohemians ahead of the 2016 League of Ireland season. He made 2 appearances for the club, a 4–3 win over Dundalk, and a 1–0 win over UCD, both in the Leinster Senior Cup.

Rooney signed for English club Millwall in July 2016. He made his Millwall debut on 8 November 2016 in a 3–1 win away to Luton Town in the Football League Trophy.

On 8 December 2016, Rooney signed a 28-day loan deal with National League club Torquay United. His loan was extended by a further 28 days on 6 January 2017.

On 24 January 2018, Rooney signed for League Two side Colchester United on a one-and-a-half year deal. He was called up to the first-team squad for the first time ahead of Colchester's League Two game against Yeovil Town on 17 March. He was given squad number 46.