 Following a string of impressive performances for Kettering Town, Dempster was signed by Crawley Town for an undisclosed fee in the 2011 transfer window, in the middle of their promotion-winning season that saw Crawley elevated to the Football League.In May 2012, Dempster was released by Crawley after being deemed surplus to requirements following a handful of League 2 appearances that year and a loan spell at Conference Premier club Mansfield Town.He signed for Mansfield permanently for the 2012/13 season.