Inverness Caledonian Thistle He made his first team debut in a friendly vs
Nairn County, scoring from 20 yards past the keeper. MacKay made his professional first team debut and scored his first professional goal against
Peterhead on 7 October 2017 in the
Scottish Challenge Cup. He scored his first
league goal in a 3–1 away loss to
Falkirk. He was assisted by fellow league debutant,
Jack Brown. MacKay is the youngest player and goalscorer in the club's history, at just 16 years and 174 days. He was one of 10 youth players to turn professional with the club in May 2018. On 9 August 2019, MacKay and goalkeeper
Daniel Hoban were loaned by Inverness to
League Two club
Elgin City. However a little over a week later, MacKay injured his ankle in a 1–0 home loss to
Stenhousemuir in the 43rd minute. MacKay's loan was extended to the end of the season in the January Transfer Window. In his first full playing season with Inverness, MacKay scored seven goals and won the club's goal of the season award for his effort against
Ross County in a Scottish Cup tie.
Hibernian MacKay signed for
Hibernian for an undisclosed amount in May 2021. On 29 July 2021, MacKay scored his first goal for
Hibernian in a competitive game against
FC Santa Coloma in a 2–1 win in the
UEFA Conference League qualifiers second-leg. On 13 January 2022, MacKay joined
Scottish Championship side
Kilmarnock on loan for the remainder of the
2021–22 season. In July 2022, MacKay was loaned back to
Inverness Caledonian Thistle for the 2022–23 season. He scored for Inverness in the
2023 Scottish Cup final, which they lost 3–1 to
Celtic. MacKay moved on loan to
Livingston in August 2023.
Partick Thistle In June 2024, he joined
Partick Thistle on a two-year deal following his departure from
Easter Road. Following an injury in training in August 2024, it was confirmed that MacKay would be out injured for a significant period of the 2024–25 season. == International career ==