Signed by Wimbledon as a youngster, whilst at Ashburton Community School, he made his way through the youth set up until breaking into the first team. Ardley made eight league appearances for Wimbledon in the 1991–92 season, featuring more prominently in the 1992–93 campaign, in which he played in 26 games and scored four goals in the inaugural season of the FA Premier League as the Dons finished 12th. Wimbledon finished 6th in the FA Premier League in 1993–94, matching the record highest ranking achieved by the club during their first ever season in the top flight during 1986–87). Ardley's contribution was more limited during this season, however, as he was selected to play in just 16 games. He scored just once in a 2–1 win over Sheffield Wednesday on 15 January 1994. He was in and out of the side for nearly a decade afterwards, remaining with the Dons after their relegation at the end of 1999–2000. Two more seasons followed as he unsuccessfully tried to help them regain their Premier League place, beforer signing for Division One rivals Watford on a free transfer on 9 August 2002.
By the time Ardley left the club in 2002 he had played a total of 245 league games for Wimbledon, scoring 18 goals. He was their longest serving player by the time of his departure. His best campaign was arguably the 1996–97 season, where he missed just four league games, helped the Dons reach the semi-finals of both the FA Cup and the Football League Cup, and oversaw an excellent season in the league where they were rarely out of the top five until having to settle for 8th place in the final table.
Ardley announced his retirement from professional football on 30 August 2007 after a series of injuries. The same day he was appointed as manager of the Cardiff City academy. Ardley had started preparing for a manager's role at the early age of 24, when he took his first coaching badges before completing his training for the UEFA Pro coaching qualification in 2010. He impressed in the role by guiding several players through to the first-team squad, including highly-rated pair Joe Ralls and Theo Wharton making the step-up. Ardley remained with the club for five years before being appointed as manager of Football League Two side AFC Wimbledon on 10 October 2012, with former Watford teammate Neil Cox being named as assistant manager on the same day.
On 2 December 2012, Ardley managed AFC Wimbledon in their first ever meeting with MK Dons, the football club formed via his former side Wimbledon's relocation to Milton Keynes. An injury-time goal saw AFC Wimbledon lose 2–1.
Ardley made additions to his squad during the January transfer window with Alan Bennett being the most notable. In March 2013, Ardley was nominated for npower League Two Manager of the Month following Wimbledon's unbeaten run. Going into the last match of the season Wimbledon were in 23rd place with only Aldershot Town below, however a 2–1 win at home to mid table Fleetwood Town saw Ardley lead Wimbledon to safety instead sending Barnet down.