After a successful run in the reserves he made his first Albion appearance as a substitute for Shaun Wilkinson in the 79th minute in a 2–0 home loss against Norwich City on 17 August 2002.

[6] Soon after the appointment of manager Mark McGhee, Harding was selected to make his full debut against AFC Bournemouth on 21 February 2004 following the suspension of Kerry Mayo.

[8] Harding remained in the starting eleven for the remainder of the 2003–04 season and helped the club gain promotion to the Championship after beating Bristol City 1–0 in the play-off final in Cardiff.

[10] After the game manager Mark McGhee defended Harding[11] and he regained his first team place and then scored his first goal for the club, in a 1–0 win over against Rotherham United.

After two seasons in which England's U21 coach Peter Taylor and a number of Premier League clubs had reportedly taken an interest in him, Harding was preparing to move on.

[17] Delays in resolving the negotiations led manager McGhee to publicly express unhappiness,[18] with Harding denying he had turned down a new deal.

[22] On 7 June 2005, Harding reportedly cut short a holiday to sign a three-year contract with Leeds United on a free transfer.

On 28 July, Leeds United were ordered to pay up to £850,000 to Brighton, with an initial payment of £450,000 and a further £400,000 dependent on appearances, international caps and promotion success.

[30] After only one season at Leeds United, Harding moved to Ipswich Town in a part-exchange deal for Ian Westlake on 4 August 2006.

[33] Harding established himself as first choice left back but despite suffering from an ankle injury that kept him out for three weeks,[34] he won two awards in the Ipswich Town Player of the Year presentations.

[35] Harding started the 2007–08 season in the first team and scored his first goal for Ipswich in a 3–1 defeat at Hull City on 29 September 2007.

[47] After serving a three match ban Harding made his return from suspension and scored against former club Leeds in a 1–0 win on 28 October 2008.

[51] Harding made one further appearance for Ipswich in a 1–0 away win at Crystal Palace[52][53] before joining Reading on loan in January 2009 for the remainder of the 2008–09 season.

[55] After talks with Ipswich's new manager Roy Keane in May 2009 Harding was told his contract would not be renewed and that he would be released by the club.

[73] On 28 July 2012 Harding joined Nottingham Forest for an undisclosed fee on a three-year contract,[74] hoping to win over the hearts of fans as a left back.

[79] After making his return to the first team against Wolverhampton Wanderers on 24 November 2012,[80] Harding managed to regain his left-back position before being injured against Bristol City on 9 February 2013.

[84] Harding played against Derby County,[85] but was barely used in the first team as Chris Cohen was preferred in the left-back position.

Harding made five appearances when Cohen was injured but then returned to the substitutes bench following the arrival of Danny Fox in January.

[89] Having initially become a first team regular under manager Stuart Pearce,[90] he was left out of the squad ahead of the match against Sheffield Wednesday in favour of Fox.

[96] Harding signed a two-year deal with National League club Eastleigh in August 2015 having turned down a move to Portsmouth, given his links with rivals Southampton.

[98] After his debut Harding established himself in the first team and made nineteen appearances until he suffered a calf injury during the first round of the FA Cup against Crewe Alexandra.

[103] In September 2016 Harding returned to Brighton, signing for National League South side Whitehawk under his former boss at Eastleigh, Richard Hill.