 He made his league debut on 14 August 2004, in a 3–1 defeat against Queen of the South at McDiarmid Park.During the 2005–06 season, Jackson was loaned out to Cowdenbeath, with whom he scored four goals in thirteen league appearances, and Forfar Athletic, scoring five goals in thirteen appearances.Jackson scored his first senior goal for St Johnstone on 5 September 2007 in their 2–0 victory over Ross County in the Scottish Challenge Cup.