[9][10] On 26 September 2020, McCormack made his League of Ireland Premier Division debut when he replaced Darragh Markey from the bench in the 75th minute of a 2–0 win over Shelbourne.
[15] With McCormack proving to be a key player off the bench for his club, making 26 appearances in all competitions over the season, he damaged his ankle ligaments playing for the Republic of Ireland U19's in October 2021,[16] which ultimately resulted in him missing the 2021 FAI Cup Final which his side won on penalties against Bohemians at the Aviva Stadium on 28 November 2021.
[17] McCormack's progress stalled at the beginning of the 2022 season under new manager Tim Clancy, having to wait until 1 April 2022 for his first appearance for the first team, while returning to play games with the club's under 19 side.
[20] Having made just 4 appearances in the club's first 11 games of the season under Tim Clancy, McCormack regained his place in the team under newly appointed manager Jon Daly and on 15 May 2023, he scored his first goal of the season, scoring an 84th-minute equaliser 11 minutes after entering the pitch in a 3–2 loss to Shamrock Rovers at Tallaght Stadium.
[22] His form under Daly saw him among the nominees for the League of Ireland Player of the Month award for June 2023, although he eventually lost out to Patrick Hoban.
[23] On 12 July 2023, McCormack made his first appearance in European competition in a 2–1 loss against F91 Dudelange in the first qualifying round of the UEFA Europa Conference League at the Stade Jos Nosbaum.
[32] McCormack scored on his debut for the Republic of Ireland U17s in a 2–0 win over Russia U17 at the Estadi Olímpic Camilo Cano in Spain.