[1][2][3] He won his first regional title on 20 November 2010, scoring a ten-round unanimous decision against Harry Matthews to become the youngest ever English middleweight champion at twenty years old.

[7] Blackwell travelled to Ukraine on 21 September 2013 to fight for the vacant WBA Continental (Europe) middleweight title, but lost a twelve-round unanimous decision to Max Bursak.

Blackwell achieved his most significant win, on a prominent stage at The O2 Arena in London, by stopping Ryder in seven rounds to become the British middleweight champion.

[8] Two successful title defences were made in the remainder of 2015, against Damon Jones on 25 July (sixth-round stoppage), and Jack Arnfield on 14 November (unanimous decision).

[9][10] In his third title defence on 26 March 2016 at Wembley Arena, which would have won him the Lonsdale Belt outright, Blackwell lost to Chris Eubank Jr.

In a fast-paced fight, Eubank Jr. dominated the action using hard hooks and uppercuts, which eventually led to a bloody nose and a large swelling above Blackwell's left eye.

In the tenth round the referee summoned the ringside doctor to assess Blackwell, who in turn deemed him unable to continue due to the swelling on his head obstructing his vision, therefore handing Eubank Jr. the victory and title.

[19] An investigation of the events was conducted by the British Boxing Board of Control, following which cruiserweight boxer Hasan Karkardi and his trainer were both suspended from their roles after their involvement in the incident.

[21][22] In June 2018, Blackwell made his first public appearance following the ill-fated sparring session, in support of his friend Tyson Fury at the press conference for his fight against Deontay Wilder later that year.