Born in London, Campbell started his career at Aston Villa as a trainee,[3] but was not offered a professional contract.

[4] In August 2002 Campbell was placed on the transfer list at his own request in order to gain regular first-team football, with club chairman Phill Wallace saying, "He's a very talented lad, and has every chance of playing higher so we won't let him go unless the terms are right for us.

At the end of the season, on 7 June 2005, Brentford manager Martin Allen signed him for the League One club for £5,000 on a one-year contract, with an option to extend it.

[11] On 28 January 2006 Campbell scored two goals to lead Brentford to a 2–1 victory over Premier League club Sunderland in the fourth round of the FA Cup.

[16] He made his Premier League debut as a substitute on 4 February 2006, playing the final twenty minutes in a 2–0 defeat to Arsenal.

[17] The club were relegated at the end of the season, and Campbell scored his first goal for them in a 2–1 win over Colchester United on 5 August 2006 in the Championship.

[18] On 25 November he scored with his first touch of the ball after coming on as an 82nd-minute substitute to give The Blues a 2–1 win over Burnley at Turf Moor.

[19] On 1 April 2007, after being included in the squad due to an injury to the club's new loan signing Andy Cole, he scored twice as a substitute as they beat local rivals Coventry City 3–0.

"[20] Campbell started 25 games for The Blues that season, scoring 12 goals in all competitions as they were promoted back to the Premier League.

[22] In his column on BBC Sport, Ian Holloway, then-manager of Plymouth Argyle, described the fee as "absolute madness".

[25] After struggling to get a regular place in the first team in League One,[3] on 8 January 2009 Campbell signed for Championship club Blackpool on loan until the end of the 2008–09 season.

"[28] After scoring his sixth goal for The Seasiders in a 1–1 home draw with Southampton on 21 March, Campbell was named in the Football League's Championship "Team Of The Week".

[36] He marked his debut for The Rams by coming off the bench to score a 94th-minute equaliser in a 2–2 home draw against West Bromwich Albion.

He described the move as fate saying, '"It's odd but I was watching the Beeb's show last Saturday night, and the bit where the lady was reading out the e-mails.

[43] On 11 May 2010, Campbell hit his first career hat trick, in a 4–3 away win in the second leg of the play-off semi-final against Nottingham Forest within the space of 25 minutes.

[44] After Blackpool beat Cardiff City in the final, Campbell expressed his desire to make his move to the seaside permanent.

Impressing new manager Paulo Sousa in pre-season by scoring in five of the six friendly matches played, he described Campbell as "someone who is going to help us a lot this season.

[53] He went on to score the equaliser against Aston Villa in an eventual 3–2 defeat, then notched another, his third of the campaign, at Stoke City on 11 December with the only goal of the game.

[6][65] On 8 February 2013, Campbell signed for Football League Championship side Blackburn Rovers on a three-month loan, to run until 12 May.

[67] On 4 July 2013, Blackburn Rovers announced the signing of Campbell from Queens Park Rangers following his release at the end of the 2012–13 season.

[67] On 9 December 2013, the club confirmed that Campbell was one of six men arrested by the National Crime Agency in connection with allegations of spot-fixing.

[71] Following his return a few days later, Rovers manager Gary Bowyer confirmed that Campbell was available for selection for future matches on the same basis as any other player.

[81] He signed for the club after being jokingly asked to by former mentor Johnson Hippolyte, but Campbell took the offer seriously as he wanted to regain his love for football after being wrongly implicated in a match fixing ring.

He made his debut for the club in the FA Cup Second Qualifying Round against Faversham Town, and scored as Maidenhead won the game 4–0.