Born in London, Rosenior started his career with Bristol City as a promising midfielder. Arguably his best moment came when he scored the second goal in a 2–0 victory for Bristol City against Carlisle United in the 2003 Football League Trophy Final at the Millennium Stadium. In the first round of Bristol City's cup run they defeated Queens Park Rangers on penalties, and it was Rosenior who scored the winning penalty in the shootout. In November 2003 he signed for Fulham. On 22 September 2004, Rosenior was sent off on his Fulham debut in a 4–1 Carling Cup second round win at Boston United when he received a second yellow card in injury time for diving. He would not make his Premiership debut for the club until 13 December when he impressed in a 1–1 home draw with Manchester United, earning him the Sky SportsMan of the Match award. Rosenior's first season at Craven Cottage would end as it began when he was sent off in a 3–1 win at Blackburn on 7 May for pushing over Robbie Savage in the 70th minute. Rosenior soon became popular amongst Fulham fans due to his Afro hairstyle. During a match against Manchester City Rosenior made a seemingly impossible goal line clearance while the score was at 1–1, Fulham going on to win the game 2–1 with Steed Malbranque scoring in the last minute. Rosenior later told reporters that he was able to clear the ball in that manner due to his Afro hairstyle. He scored once for Fulham, in a League Cup tie against Lincoln City on 21 September 2005. of Aston Villa in 2014 He signed a four-year extension to his Fulham contract in July 2006, but left Fulham for Reading on 31 August 2007 for an undisclosed fee on a three-year contract, with Seol Ki-Hyeon going the other way. His debut for Reading came in a 2–1 defeat to Sunderland on 15 September 2007, and he scored his first goal for Reading in a 7–4 defeat to Portsmouth on 29 September 2007, although it was initially awarded to Stephen Hunt. On 2 September 2009 Rosenior joined Ipswich Town on loan for the remainder of 2009–10 season. He scored his first goal for Ipswich against Barnsley on 3 October 2009.
Hull City
On 29 October 2010 Rosenior joined Hull City on a short-term agreement until 1 January 2011. He made his debut the following day in the away match at Barnsley. He signed a -year deal with Hull on 21 December 2010. Saying "I'm delighted, It's something that we kind of half agreed when I first came here, but it relied on the takeover being completed for me to stay."
2013–14 season
On 18 August 2013, Rosenior was an unused substitute as Hull lost 2–0 against Chelsea at Stamford Bridge on the opening weekend of the season. On 22 March 2014, Rosenior scored his only goal for Hull City when heading the rebound in from a Nikica Jelavić penalty that was saved by West Bromwich Albion goalkeeper Ben Foster. On 17 May 2014 he started in the 2014 FA Cup Final against Arsenal. On 28 May 2015, Hull City released Rosenior and five other players who were out of contract at the end of the 2014–15 season.
Brighton & Hove Albion
On 23 June 2015, Rosenior signed for Brighton & Hove Albion on a three-year deal following his release from Hull City. He retired from playing on 30 July 2018.
Coaching career
Brighton & Hove Albion
Following his retirement from playing, Rosenior remained at Brighton, taking up the position of assistant coach with Brighton's under-23 team, which he combined with appearing as a pundit on Sky Sports.
On 10 July 2019, Rosenior was appointed as specialist first team coach to Phillip Cocu at Derby County.
International career
Rosenior was born in England, and is of Sierra Leonean descent through his father, Leroy Rosenior, who was an international footballer for Sierra Leone. Rosenior was called up to the England U21 squad in March 2005, and made his debut in a 2–2 draw with Germany U21 on 25 March 2005, closely followed by a second cap in a 2–0 win over Azerbaijan U21 on 29 March 2005 His performances earned him a call up to the England U20 squad for the Toulon Tournament in June 2005, where he played three times and scored one goal. However, it would be over a year and a half before he would add to his England U21 caps, with the next one coming against Netherlands U21 on 14 November 2006. Rosenior made it into the squad for the 2007 UEFA European Under-21 Championship, but only made one appearance, as a substitute in the semi final against Holland U21. He took part in the shootout in this game, scoring his penalty as England lost 13–12. Due to his age, this would prove to be his seventh and last appearance for the England U21 team.
