A product of the Manchester United academy, during his development Simpson played on loan for Sunderland, Ipswich Town and Blackburn Rovers in England, and Royal Antwerp in Belgium. He was on loan at Newcastle United for six months before signing for them on a permanent basis in January 2010, and after four years joined Queens Park Rangers on a free transfer in June 2013 for a year, before joining Leicester City the following season.
Simpson was born in Eccles, Greater Manchester, to a Jamaican father and English mother. Simpson played for Parkwyddn JFC in Eccles as a youth before being picked up by Manchester United. He is a product of the Manchester United youth system, having come up through the ranks into the reserve squad in 2005.
Simpson made his debut against South African team Kaizer Chiefs on 18 July 2006, which the Reds won 1–0. Manager Alex Ferguson claimed that Simpson looked "anything but a player making his first start for Manchester United".
In early January 2006, he was sent on loan, along with three other United youths, to the Belgian second division club Royal Antwerp for the remainder of the season, to gain match experience. Simpson also spent the first half of the 2006–07 season at Antwerp before returning to United in January 2007.
On 25 January 2007, he joined Sunderland on loan for the rest of the season. The loan move saw him link up with fellow Manchester United player Jonny Evans. He won the Championship title with Sunderland that season.
Simpson returned to United at the start of the 2007–08 season and signed a new contract in September 2007 that would keep him at the club until 2010. He made his first competitive appearance for United on 26 September 2007 in the 2–0 League Cup loss to Coventry City, and soon after made his Premier League debut on 6 October 2007 against Wigan Athletic at Old Trafford, coming on as a 30th-minute substitute for the injured John O'Shea. He set up the fourth goal with a well flighted cross for Wayne Rooney. The match ended with a 4–0 win to United. His European debut came on 23 October 2007, when he came on as an 80th-minute substitute for Ryan Giggs against Dynamo Kyiv. His first European start was in the reverse fixture against Dynamo Kyiv on 7 November 2007; United won the game 4–0.
On 21 March 2008, Simpson signed a loan deal with Ipswich Town. With Gary Neville on the verge of returning to the Manchester United first team, United manager Alex Ferguson decided it was best for Simpson to get as much first team football as possible, something that would be quite hard to come by at Old Trafford with both Gary Neville and Wes Brown ahead of Simpson in the pecking order.
On 4 August 2008, Simpson signed for Blackburn Rovers on a season-long loan deal. Simpson made his Blackburn debut on 27 August 2008, playing in Rovers' 4–1 win over Grimsby Town in the League Cup Second Round. His Premier League debut for Blackburn Rovers came almost three weeks later, on 13 September 2008, in a 4–0 defeat at home to Arsenal. With the exception of Blackburn's League Cup Fifth Round defeat by Manchester United, which he was forced to miss because of a clause in his loan agreement, Simpson was ever-present for Blackburn during their League Cup and FA Cup campaigns. He also played in 11 out of the 14 league matches for which he was eligible prior to Christmas 2008, although he was named on the bench for the other three. After Christmas, Simpson only played in one further league match, another 4–0 defeat to Arsenal, and in early May 2009, with his first team opportunities limited at Blackburn, the loan agreement was terminated early and he returned to train with Manchester United.
On 14 August 2009, Simpson joined Newcastle United on loan until January 2010, making his debut in a 1–0 victory over Sheffield Wednesday at St. James' Park. He scored his first goal for Newcastle against Peterborough United on 7 November 2009.
Following the completion of the loan deal, Newcastle made a bid to keep Simpson on a permanent basis. An undisclosed fee, reported as being in the region of £750,000, was agreed between Newcastle and Manchester United and Simpson signed a three-and-a-half-year contract on 20 January 2010.
He played a solid part in Newcastle's promotion to the Premier League, winning his second Championship title in the process, while forming a right flank partnership with January signing Wayne Routledge. Towards the end of the season, he "played through the pain" with what he considered a small ankle injury. He only realised the full extent of the ankle injury at the end of the season, and he had an operation to correct it. He was out for three months, including the first month or so of Newcastle's season. Simpson returned to action from his injury lay off, playing two reserve games in October. He made his first start of the new season in Newcastle's 2–1 victory over West Ham United, replacing James Perch at right-back. Simpson kept his right-back spot with consistently strong performances, forming a strong partnership with Joey Barton on the right flank.
On 20 September 2011, Simpson scored a curler in Newcastle's 4–3 win over Championship side Nottingham Forest in the third round of the League Cup.
On 10 December 2011, Simpson started alongside James Perch at center back in place of the injured Steven Taylor and Fabricio Coloccini for Newcastle's 4–2 defeat at Norwich City. He had played at right-back for the beginning of the season.
On 4 January 2012, Simpson started for Newcastle during their 3–0 win against Manchester United, and produced a fantastic saving clearance off the line against his old club on his 25th birthday.
After his contract with Newcastle expired at the end of the 2012–13 season, Simpson signed a three-year deal with Championship club Queens Park Rangers on 27 June 2013. He scored his first goal for QPR in a League Cup tie against Exeter City on 6 August 2013. He made 36 Championship appearances for QPR as they earned promotion via the play-offs.
On 30 August 2014 signed a three-year contract for fellow promoted team Leicester City for an undisclosed fee. Simpson made his Leicester debut in a 2–0 defeat against Crystal Palace off the bench on 27 September 2014. However, he didn't make his second appearance for the club until 7 December against Aston Villa, as he often struggled to get into the side ahead of regular right-back Ritchie De Laet. Simpson made 14 appearances overall for Leicester in the 2014–15 season.
In the 2015–16 season, under the new management of Claudio Ranieri, De Laet was again preferred ahead of Simpson to begin with. However, following a 5–2 defeat by Arsenal, Ranieri changed his full-backs bringing Simpson in for De Laet helping to sure up Leicester's defence, as Simpson was considered a much more defensive full-back than De Laet and "rarely ventured forward". Simpson became a regular for the rest of the season, though was sent-off in the return fixture against Arsenal as Leicester went down to a late 2–1 defeat, but the Foxes held on to win their first ever Premier League title.
Simpson has a daughter called Skye, born six weeks prematurely in mid-2011.
On 20 May 2015, Simpson was found guilty of assaulting his then-girlfriend and mother of his child Stephanie Ward on 28 December 2014. He was sentenced to 300 hours of community service. On 12 May 2016, his sentence was reviewed in light of press-intrusion into his community service, and replaced with a 22:00 to 06:00 curfew for 21 days.As of 19 September 2017
Newcastle UnitedChampionship: 2009–10
Queens Park RangersChampionship play-offs: 2013–14
Leicester CityPremier League: 2015–16