After being released by Celtic in February 2003, Millar signed for then Scottish Football League Third Division side Greenock Morton. Millar made his Morton debut away at Montrose on 25 February 2003. On 21 December 2007, it was announced on Greenock Morton"s website that Millar had signed a pre-contract agreement with Street Johnstone.
He officially signed with the club on 1 May 2008.
He signed a two-year contract with Street Johnstone in January 2015.
He was a member of Morton"s 2002-2003 Scottish Third Division championship-winning team that season.