He made his international debut for the Irish cricket team in February 2019. In January 2020 he was one of nineteen players awarded a central contract by Cricket Ireland, the first year that all contracts were awarded on a full-time basis.

Domestic Career

He made his first-class debut for Durham MCCU against Gloucestershire in the Marylebone Cricket Club University games on 28 March 2017. Prior to his first-class debut, he played for the Northern Knights at the 2016 Inter-Provincial Championship in Ireland.

On June 23, 2017, he made his Twenty20 debut for Northern Knights at the 2017 Inter-Provincial Trophy. On August 6, 2017, he made his List A debut for the Northern Knights at the 2017 Inter-Provincial Cup. He was the Northern Knights' leading runs scorer in the 2018 Interprovincial Championship with 442 carries in four games.

International Career

In December 2018 he was one of nineteen players awarded a pivotal contract by Cricket Ireland for the 2019 season. In January 2019 he was called up to Ireland's Test and One Day International (ODI) squads for their series against Afghanistan in India.

He made his ODI debut for Ireland against Afghanistan on 28 February 2019. He made his Test debut for Ireland on March 15, 2019 against Afghanistan.

In June 2019 he was called up to the Ireland Wolves squad for their home series against cricket team Scotland A. On 10 July 2020, McCollum was called up to Ireland's 21-man squad to travel to England and begin behind closed doors training for the ODI series against England cricket team.

In February 2021, McCollum was called up to the Ireland Wolves squad for their tour to Bangladesh.