*Club domestic league appearances and goals, correct as of 14:07, 8 August 2024 (UTC) ‡ National team caps and goals, correct as of 23:54, 27 September 2022 (UTC)
Tierney spent his youth career with St. Kevin's Boys (which was amalgamated with Bohemians in 2018) from the age of eight.[1] Having progressed through the Bohs-SKB U17s and U19s teams, Tierney came to prominence in the second half of the 2019 season with his displays.[citation needed]
He made his first-team debut in the League of Ireland Cup Quarter Final clash with Cork City in May 2019, scoring the opening goal in a 2–0 win.[2] He struck a further three times during his rookie season, hitting the net against UCD,[3]Dundalk[4] and Waterford.
After notching seven goals and fifteen assists during the 2021 campaign, Tierney, alongside teammate Dawson Devoy and UCD's Colm Whelan, was nominated for the PFAI Young Player of the Year award.[6]
Motherwell
On 1 December 2021, Tierney signed with Motherwell for an undisclosed fee on a three-and-a-half-year deal.[7] He completed the move on 1 January 2022. Tierney made his debut for the club on 22 January 2022 in a Scottish Cup tie against Greenock Morton, coming off the bench in the 76th minute and winning a penalty as his side won 2–1 in extra time. His first goal for Motherwell came on 1 February where he netted a 92nd minute equaliser in a 1-1 draw against St Mirren.
His second goal came at home to Rangers.[8][9]