[12] After making his league debut against Accrington Stanley his hopes of regular first team football were dashed by a pre-season injury that kept him out of action for several months.

[13] Blackman joined Premier League club Blackburn Rovers on 12 January 2009, after impressing in a trial, for an undisclosed fee on a two-and-a-half-year contract.

[22] Blackman joined Scottish Premier League club Motherwell on a six-month loan on 13 August 2010[23] and scored 10 goals in 18 games in total which, included a hat trick in a 4–0 win over St Johnstone in November 2010.

During the Premier League Asia Trophy match against Kitchee of Hong Kong, Blackman came off the bench for Blackburn and won and converted a penalty in a 3–0 win.

On 10 August 2012, Blackman signed for Sheffield United on a two-year deal for an undisclosed fee reported to be £115,000 plus a 20% sell on after turning down offers from Championship clubs.

[26] Blackman scored his first goal for the Blades with his first touch in a League Cup game against Burton Albion at Bramall Lane on 11 August 2012.

[36] After starting only 12 matches for Derby, Blackman joined Israeli Premier League club Maccabi Tel Aviv on a season-long loan in August 2017.

Despite some favourable displays in the early part of the season, Blackman spent large amounts of time away from the first team due to injury.

[41] Blackman scored both goals for Maccabi in the first leg of their victory against Hapoel Be'er Sheva in the Israel Super Cup on 8 August 2020.

[47] Blackman made his debut for Barbados on 5 September 2019, scoring a brace in a 4–0 win over Saint Martin in a CONCACAF Nations League match.