Forster, who was born in Caterham, Surrey, was spotted playing for non-league Horley Town and invited for trials by Gillingham in December 1991.
Forster receives part of the credit for salvaging Reading's 1999–2000 season, during which the club rose from Division Two's relegation zone at Christmas to a finish in the top ten under caretaker manager Alan Pardew.
He set up Martin Butler for the equaliser before winning a penalty; after Jamie Cureton's effort was saved, Forster scored from the rebound.
Unable to replicate for Ipswich the form he showed with Reading due to several injury setbacks over the 2005–06 season, Forster signed a two-year contract with Hull City on 31 August 2006 for a £250,000 transfer fee.
[10] However, at the end of the 2006–07 season, Forster stated his wish to move back to the south of England for family reasons,[11] and eventually signed a three-year contract with Brighton in late June 2007 for a £75,000 fee.
[12] He attributed his decision to drop down to Football League One from the Championship to the ambition shown by Brighton manager Dean Wilkins and chairman Dick Knight.
[13] Forster was appointed club captain after the departure of Dean Hammond during January 2008, and confirmed in the role by new manager Micky Adams for the 2008–09 season.
[16] Having lost his first-team place after a contract dispute with manager Gus Poyet, Forster left Brighton for Charlton Athletic on 25 March 2010 on loan until the end of the season.
[26] In January 2013, with Dover still third in the table despite five consecutive losses, Forster was placed on gardening leave; the club appointed Chris Kinnear the following day.
[27] Forster was appointed as the replacement for Marcus Gayle as manager of Staines Town on 8 January 2015, with the task of keeping them in the Conference South.