He previously played for Dunfermline Athletic, Albion Rovers (loan spell), East Fife twice, Queen of the South, Falkirk, Edinburgh City and Bonnyrigg Rose.
Born in Kirkcaldy,[2] Mercer began his career with Dunfermline Athletic in 2005, progressing through the club's youth set-up.
[5] After the Pars went into administration in 2013, Mercer played once for the club in a Scottish League One match versus Rangers, coming on as an 82nd minute substitute for Craig Dargo.
[10] In his first season, Mercer was ever-present in the Methil club's defence, playing a total of 41 matches and scoring one goal versus Montrose.
[14] On the same day, Mercer sustained a broken foot after 16 minutes of Queens final league match of the 2017-18 season at Glebe Park versus Brechin City.