Celtic Born in
Stirling, McMullan began his career in the under-19 team at
Celtic.
Stenhousemuir (loan) On 23 January 2015, he joined
Scottish League One club
Stenhousemuir on loan for the remainder of the season. He made his senior debut the following day, playing the full 90 minutes of a 1–1 draw with
Ayr United at
Ochilview Park, scoring his team's goal. On 14 February, he opened the scoring away to
Dunfermline Athletic, who came from behind to defeat Stenhousemuir 3–2. McMullan's only other goal of 14 league appearances came on 11 April in a defeat by the same score at
Greenock Morton. Stenhousemuir finished in the relegation play-off places, but stayed up with a 2–1 aggregate victory over
Queen's Park: McMullan's free-kick set up
Jamie McCormack to head the only goal of the first leg on 13 May, and he also assisted
Colin McMenamin in the second leg three days later.
St Mirren (loan) On 13 July 2015, McMullan was loaned to
Scottish Championship club
St Mirren for the
2015–16 season. He made his debut 12 days later, playing the full 90 minutes of a 3–1 home win over
Berwick Rangers in the first round of the
Scottish Challenge Cup. On 7 August, he made his league debut for the team in a defeat by the same score to
Rangers at
Ibrox. Twenty-two days later, he scored his only goal for the team from
Paisley, taking four minutes to open a 1–1 draw against
Livingston at
St. Mirren Park; the result meant his team had not won yet in four league games of the season. In January 2016, McMullan's loan was ended by Saints, and he returned to Celtic. In total, he played 22 games for the club, scoring once.
Greenock Morton (loan) McMullan was loaned to
Greenock Morton on 24 February 2016, making his debut in a 3–0 Championship win at
Hibernian on the same day. On 15 March at
Cappielow, he scored his first goal for the Ton, putting them 3–0 up at half time in an eventual 3–2 win over
Queen of the South.
Dunfermline Athletic (loan) On 4 July 2016, McMullan was loaned to newly promoted Championship team
Dunfermline Athletic, as
PJ Crossan made the move in the other direction on a permanent basis.
Dundee United On 23 June 2017, McMullan signed a two-year contract with
Dundee United.
Dundee On 7 January 2021, McMullan signed a pre-contract with United's
crosstown rivals Dundee, which would see him begin a two-year deal at the end of the season. On 26 January, McMullan joined Dundee on loan until the end of the season. Despite only joining in January, McMullan would sit atop the league assist charts by the end of the season, and would play a key role in helping the club win the
Premiership play-offs and gaining promotion back to the
Scottish Premiership. At the end of the season, McMullan was named in the
SPFL's Championship Team of the Season. McMullan officially joined Dundee on his two-year deal in June 2021. He would score his first competitive goals for the club in the
Scottish League Cup, netting a brace against
Brora Rangers. On 5 March 2022, McMullan would finally score his first league goal for the club since he joined over a year prior in a draw away to
Motherwell. After returning to the
Scottish Championship the following season, McMullan would have a very strong start in both goals and assists, and would be named the
Championship Player of the Month in November 2022. At the end of the season McMullan would be nominated for
PFA Scotland's Championship Player of the Year, and would win the
Scottish Championship with Dundee. On 31 May 2023, Dundee announced McMullan had not been offered a new contract and would leave the club.
Derry City On 25 June 2023, McMullan signed with
League of Ireland Premier Division club
Derry City, and would start playing for the side on 1 July. He would make his first start and appearance in a home win over
Sligo Rovers. McMullan scored his first goal for the
Candystripes on 6 May 2024 in a league draw against
Shelbourne. On 30 June 2025, it was reported that McMullan had left Derry in favour of a move back to Scotland.
Raith Rovers On 1 July 2025, McMullan returned to Scotland and joined
Scottish Championship club
Raith Rovers on a two-year deal.
International McMullan represented Scotland at the
under-16,
under-17,
under-19 and
under-21 levels. He made his debut for the under-21 team in March 2017, appearing in a goalless draw against
Estonia. ==Career statistics==