Having come through the youth academies at Celtic and Blackburn Rovers he would notably play in the Scottish Premiership for Kilmarnock, Dundee and St. Mirren.
[19] Harkins then moved to his native Scotland, and after a trial signed a one-year contract with Scottish First Division club Partick Thistle in July 2007.
[26] At the end of the season, Harkins was offered a new contract with the club,[27] but he reportedly rejected a deal, something that was denied by Ian McCall.
[35] He made a further 38 appearances, scoring five goals, in a troubled 2010–11 season for Dundee in which the club was penalised 25 points by the Scottish Football League in November 2010 after going into administration.
[41][42] He made his first appearance for the Ayrshire side on 24 July, in a 1–1 draw with Dundee United at Tannadice and scored his first goal for the club in a 5–0 win over Queen of the South in the Scottish League Cup 3rd round, only 90 seconds into the match.
During January 2013, it was reported that he could return to Dundee; this was initially denied by manager Kenny Shiels, who claimed that Harkins was "one of the best players in the SPL".
[47] Following their relegation, Harkins said his future was uncertain as he wanted to play at the higher level[48] and soon announced his departure, citing the club's failure to agree a change of ownership.
[54] A few weeks later, Harkins was criticised by manager Danny Lennon for not "working hard enough off the ball to succeed at St Mirren".
[58] After Harkins' loan spell at Oldham Athletic came to an end, St Mirren announced on 27 June 2014 that the midfielder had his contract with the club cancelled by mutual consent.
On 12 August 2016, it was confirmed that Harkins had signed a two-year contract as a player/coach with newly promoted Scottish Championship club Ayr United.
[74] Harkins signed for Partick Thistle for a second spell on an 18-month contract on 27 December 2018, three days after leaving Queen of the South.
[75][4] Harkins scored his first goal in his second spell at the Jags in a 4–1 win away at Stenhousemuir in the quarter final of the Scottish Challenge Cup.
[80] In June 2021, Harkins was appointed as the first team coach for Scottish League Two side Forfar Athletic underneath manager and former Dundee teammate Gary Irvine, as well as being registered as a player.
[82] On 11 November 2022, following the sacking of Irvine and the hiring of new manager Ray McKinnon, Forfar announced that Harkins had departed the club.
[83] On 6 December 2022, Harkins joined West of Scotland Football League First Division club Kilbirnie Ladeside as a player-coach under manager Shaun Dillon.
[86][87] Harkins was born in Greenock[88] and attended St Columba's High School, Gourock, where he played in a wide variety of positions and for various teams before signing for Blackburn Rovers.