Barker began his playing career with Sheffield Wednesday but, after just the one senior appearance and two loan spells away at Doncaster Rovers and Ards, he joined Northern Ireland outfit Linfield in 1997.
After a short stay with the Blues, Barker returned home to sign for Brighton & Hove Albion, where he would go on to score 23 goals in 103 appearances before joining Macclesfield Town on a free transfer in June 1999.
Barker tallied 26 goals in 68 games in two seasons at Moss Lane, form which earned him a £60,000 move to Division One side Rotherham United in 2001.
Featuring 155 times for the Millers and helping them win promotion to the Championship in his first season, Barker was allowed to join Mansfield Town on a free transfer in 2004 after mainly being used as an impact substitute.
The prolific frontman scored 48 goals in 106 games with the Stags and became a fans favourite with the Stags’ faithful before eventually joining Hartlepool United in January 2007 for a reported fee of £80,000.
Barker netted 27 times in 73 games for the Pools before re-joining Rotherham in 2008 where he would later retired due to a knee injury just a year later.
After joining Sheffield United as an academy coach, Barker was named Bury’s youth-team manager in July 2010. Barker then stepped up to the role of caretaker manager of the Shakers after Alan Knill left for Scunthorpe United with just eight games remaining in the 2010/11 season.
Barker led Bury to six consecutive victories that season which saw them win promotion to League One and Barker appointed permanent manager at Gigg Lane.
The following summer, Barker was named manager of Crawley Town and he led the Red Devils to 10th place in his and their first season in Sky Bet League 1 before leaving in November 2013.
Just a month after his departure from Memorial Stadium, Barker was presented as Portsmouth manager with Steve Coppell being appointed as director of football.
Barker left Fratton Park after 20 games in charge before taking up a an adivsory role alongside Robinson at Stadium MK in April - a role which was made permanent the following month.
During his first full season at Robinson's assistant he helped lead the Dons to an automatic promotion berth in League 1.