In October 2011, Blackman had a trial with Scottish Premier League side Celtic, playing his first match in a year when Celtic’s development squad played a bounce game against a Rangers XI. This trial resulted in Blackman signing for Celtic in November 2011. He made his debut for Celtic on 3 March, in a 1–1 draw with Aberdeen. Although not featured enough at Celtic, the club won their first title in over 4 years.
Blackman thanked Neil Lennon for saving his football career after a troubled year and admitted he had to show humility and mental strength to make a breakthrough.