*Club domestic league appearances and goals, correct as of 17:15, 15 January 2025 (UTC) ‡ National team caps and goals, correct as of 17:15, 15 January 2025 (UTC)
A native of Thomastown, County Kilkenny, Whelan began playing with his local club Thomastown United, before moving to the academy of Waterford in 2016, where he played for the under 17 side for two seasons before making his first team debut.[2]
Whelan signed for League of Ireland First Division club UCD ahead of the 2020 season and scored on his debut on 16 February 2020 in a 1–1 draw away to Wexford at Ferrycarrig Park.[6] Whelan had an impressive first full season at senior level, scoring 15 goals in 21 appearances in all competitions.[7] The 2021 season proved to be even more impressive, both individually and collectively, as scored 25 goals in 31 games in all competitions, culminating on 26 November 2021 with Whelan scoring the winner in a 2–1 victory over his former club Waterford in the League of Ireland Promotion/Relegation Playoff Final at Richmond Park.[8] Whelan was named League of Ireland Player of the Month for November 2021.[9]
On 21 December 2021, following the club's promotion, Whelan turned down offers from elsewhere within the league, to sign a new contract with UCD in order to complete his degree at the college.[10] Whelan scored 4 goals in 15 games in the first half of the 2022 season, with his performances attracting interest of several English clubs including Lincoln City, but an Anterior cruciate ligament injury suffered in a 1–0 win away to Finn Harps on 13 May 2022 scuppered any move for the striker in the short term.[11]
Whelan received his first call up to the Republic of Ireland U21 team in May 2021.[24] He made his debut for the side on 9 September 2021, scoring in a 1–1 draw away to Luxembourg U21.[25] On 12 November 2021, his third and final appearance for the side was his first start at international level, in a 2–0 loss at home to Italy U21.[26]