Born in Coniston, Lancashire, Edmondson started as a trainee at Carlisle United, where he stayed for seven years before being transferred to Huddersfield Town for £225,500. He had a difficult time there however, he even scored a bizarre own goal against Ipswich Town, in which he was passing the ball back to Town's keeper Steve Francis and it somehow went through his legs and into the goal.
He went to York City in 2000, before leaving to Chester City after York's relegation to the Football Conference. He spent just one year at Chester and joined non-League side Barrow under Lee Turnbull. After Turnbull was sacked Edmondson had a brief spell as caretaker manager before the appointment of Phil Wilson. Wilson set about bringing in his own players and Edmondson left Barrow and signed for Workington. He made his debut for Workington on 7 January 2006 at Worksop Town. He scored his first goal for the club at Alfreton Town on 14 March.
On 5 November Workington manager Tommy Cassidy resigned to take over at Newcastle Blue Star, taking with him his number two Tony Elliott. The Workington board acted quickly and appointed Edmondson as caretaker manager on the very same day. He was later given the job on a full-time basis and was officially announced as manager at the home tie against Redditch United on 6 October 2007.
On 10 December 2013, Edmondson resigned from his post as Workington manager, following a day of change at Workington with the chairman resigning. Within hours of the resignation he was appointed Barrow manager.