Manchester United Blackett began his football career with youth club
Fletcher Moss Rangers, and signed for
Manchester United in 2002 at the age of 8. He signed a professional contract with United in July 2012.
Blackpool (loan) On 1 November 2013, Blackett signed for
Championship club
Blackpool on a month-long loan. The next day, he made his debut for the Seasiders, playing the whole 90 minutes in a 1–0 league win at
Nottingham Forest. On 5 December 2013, Blackpool extended Blackett's loan until 1 January 2014.
Birmingham City (loan) On 31 January 2014, Blackett signed for Championship club
Birmingham City on a youth loan until the end of the season. Together with fellow Manchester United loanee
Tom Thorpe, Blackett started the next day's match, at home to
Derby County. After 38 minutes, he tripped
Will Hughes to concede a penalty, which
Darren Randolph saved. Birmingham came back from 3–1 down to draw, the equaliser scored by a third United loanee,
Federico Macheda, in stoppage time.
2014–15 season: Return to United During the 2014–15 pre-season, Blackett played at centre-back for Manchester United in a 3–5–2 formation and his performances led to him earning praise from new manager
Louis van Gaal. In the club's final pre-season match against
Valencia at
Old Trafford, he provided the assist for
Marouane Fellaini's stoppage-time winner to make the score 2–1. As a result of an injury crisis and the departure of experienced defenders
Rio Ferdinand and
Nemanja Vidić from the club, Blackett was drafted into the first team squad on a permanent basis. Blackett made his competitive debut for Manchester United on 16 August 2014, in the first match of the
2014–15 Premier League season, playing the full 90 minutes and being booked in a 2–1 home defeat to
Swansea City in Van Gaal's first competitive match as Manchester United manager. He also played in the next game away at
Sunderland, which ended in a 1–1 draw with Blackett making an important clearance during the match to help earn Manchester United a point. Blackett also played in the 0–0 draw against Burnley on 30 August 2014. During the game he received a yellow card for a mistimed challenge. Blackett then played in United's first win of the season when they beat
Queens Park Rangers 4–0 as a centre-back rather than a full-back. He was sent off in the 82nd minute on 21 September as United lost 5–3 at
Leicester City. On 17 May 2015 in a home match against
Arsenal, Blackett came on in place of
Marcos Rojo after 73 minutes, and nine minutes later deflected a
Theo Walcott cross for an
own goal past United goalkeeper
Victor Valdés to cause a 1–1 draw. In total, Blackett made 12 Premier League appearances during the 2014–15 season.
Celtic (loan) On 29 August 2015, Blackett was loaned to
Scottish Premiership club
Celtic until the end of the 2015–16 season. Blackett dropped out of the side for a few matches, but returned on 4 October for a league match at
Hamilton Accies, taking the place of the suspended
Efe Ambrose in central defence and helped Celtic to a 2–1 win.
Reading On 22 August 2016, Blackett signed a four-year contract with Championship club
Reading. Head coach
Jaap Stam, a former Manchester United player, praised the defender for his versatility and attacking presence. With his contract with Reading due to expire on 30 June 2020, and due to the effects of the
COVID-19 pandemic on the
2019–20 season, Blackett signed a short-term extension with Reading until the end of the season. Following the completion of the 2019–20 season, Reading announced that Blackett would leave the club at the end of July 2020.
Nottingham Forest On 15 August 2020, Blackett joined
Nottingham Forest on a permanent contract. He made his debut for the club on 12 September, starting in a 2–0 defeat away to
Queens Park Rangers.
FC Cincinnati On 6 August 2021, Blackett joined
Major League Soccer club
FC Cincinnati on a free transfer. Blackett was released by Cincinnati following their 2022 season.
Rotherham United On 8 March 2023, Blackett returned to England when he joined Championship club
Rotherham United on a short-term contract until the end of the season. On 7 May 2024, after the club were relegated, Rotherham announced the player would be released in the summer after his contract expired.
New Mexico United On 2 March 2026,
New Mexico United announced they had signed Blackett to a contract for the remainder of the 2026
USL Championship season. ==International career==