Barr played in the early part of his career with Gretna signing for the club when they were bankrolled by Brooks Mileson. He was part of the squad who won the Scottish Football League First Division in the 2006–07 season which earned them promotion into the SPL. In 47 league appearances for Gretna, Barr scored five goals. Mileson pulled the plug on the club's cashflow when his health deteriorated. The club thus became financially stricken and went into administration. Administrators for Gretna laid off their last 40 staff including Barr on 19 May 2008.
Barr signed a two-year contract with Dumfries-based First Division side Queen of the South on 26 June 2008. Just after signing, Barr said "I'm really looking forward to the move. Queens are coming off the back of a fantastic season and I'm excited at the prospect of playing for the Scottish Cup finalists. I know big Neilly MacFarlane, Jamie McQuilken and 'Tosher' from my time at Gretna and also have a lot of respect for ex-Queens player, big Derek Townsley, who I also know well". After playing over thirty games in his first season with the club, Barr suffered a season-ending injury on his knee during the pre-season of 2009–10. He had two operations on this injury, with the major one being a complete cruciate reconstruction. As Queens refused to pay for the operation, Barr took it upon himself to fund it. Due to this matter, he then spent the last six months of his contract doing his own rehab away from the club. Barr was among the players announced as released by the club at the end of the 2009–10 season.
Livingston
Barr signed for Livingston in August 2010. In his first season, he played a pivotal role in helping the club to win the Second Division title. He subsequently signed a new two-year deal, keeping him at the club until the end of season 2012–13. Barr left Livingston at the end of the 2012–13 season, following a relatively successful three-year spell with the club making 112 appearances in all competitions.
On 23 February 2014, Barr returned to Scottish football, signing for Airdrieonians on a contract until the end of the 2013–14 season.
Raith Rovers
In summer 2014, Barr joined Raith Rovers. He left the club in June 2017, following their relegation to Scottish League One.
Dumbarton
Having left Raith, Barr joined Scottish Championship side Dumbarton on a one-year deal in June 2017. He scored his first goal for the club in a 2–1 defeat to Clyde in July 2017. He won the club's Players' Player of the Year award in his first season at the Rock and captained the side on a number of occasions. Barr turned down a new deal and left the club in May 2019 after an injury hit second season.
