Blackman began his playing career at Macclesfield Town before joining Blackburn Rovers in 2009 and spending loan periods at Blackpool, Oldham Athletic, Motherwell and Aberdeen.

Eleven goals in 28 appearances for Sheffield United led to a switch to Reading for which Blackman scored 18 goals in 103 appearances between 2013 and 2016 when he joined the Rams.

In the summer of 2017, the striker joined Maccabi and made 40 appearances across all competitions including 5 in the Europa League Group Stages. Blackman scored the sining goal in a 1:0 victory over Villarreal on the last Matchday of continental play. The striker scored 12 goals, added 5 assists and won the Toto Cup. Following the season and loan, Blackman returned to Derby.