Allan began his career in Scotland with Dundee United, and spent time on loan with Forfar Athletic, before joining English Premier League club West Bromwich Albion in 2012.

He never broke into the first team, and after loan spells with Portsmouth (twice), Milton Keynes Dons and Birmingham City, he was released at the end of the 2013–14 season.

Allan spent the next two seasons contracted to Arbroath, and also went on loan to Northern Irish club Larne, with whom he won the NIFL Premiership.

[10] After returning to United, Allan was named on the bench for four Scottish Premier League (SPL) fixtures during the 2010–11 season but did not make an appearance.

[12] He made his SPL debut on 31 July 2011 against Heart of Midlothian at Tynecastle Stadium in an away victory for Dundee United, playing 83 minutes.

[19] His debut in English football came on 25 February for Portsmouth, when he featured in the starting line-up playing 76 minutes in scoreless draw at home to Leeds United.

[33] He made his debut as a second-half substitute in a 1–0 defeat at home to Watford on 3 August, and scored twice as Birmingham beat Plymouth Argyle 3–2 after extra time in the League Cup three days later.

[11] He made no first-team appearances after August[34] until receiving a surprise recall to the squad, playing in two of the last three League matches of the season.

[11][35] West Bromwich Albion chose not to take up the option of extending Allan's contract for another year, and he was released at the end of the 2013–14 season.

[37] Allan made his debut for Hibs on 5 August 2014, coming on as a substitute during extra-time in a 2–1 defeat against Rangers in the Scottish Challenge Cup.

Although Allan also submitted a transfer request, Hibernian turned down all these bids as they were reluctant to sell him to their main rivals for promotion.

[48] He made his debut on 22 August, coming on as a substitute during the second half of Celtic's 3–1 league win away at Dundee United.

[61] The move did not go well for Allan; he was dropped from the team in October 2016 with manager Alan Stubbs publicly criticising the player for lack of effort.

[64] He made his debut on 18 July in a 2–1 win over Raith Rovers in the Scottish League Cup, providing assists for both Dundee goals.

[66] In his first game back with Hibs on 3 February 2018, he won the penalty which led to their winning goal in a 2–1 victory over Rangers at Ibrox.

[72][73] He resumed training in early December, although manager Jack Ross would not put a timescale on Allan playing in a match.

[80] On 23 August 2023, after failing to nail down a regular place at Gayfield, Allan joined Northern Irish club and reigning NIFL Premiership champions Larne on a season-long loan.

[84] After leaving Arbroath in the summer, Allan joined Scottish League One club Kelty Hearts on a permanent deal in July 2024 as both a player and the first team coach under manager Michael Tidser.

[85] Allan made his competitive debut on 16 July in a Scottish League Cup group stage game away to Elgin City.