Mike Fillery began his career as an apprentice with Chelsea, turning professional in August 1978, having won England schoolboy and youth honours. He made his league debut later that season, as a substitute in a 1-1 draw at home to Derby County on April 4, 1979.
He went on to play 159 games, scoring 32 goals for Chelsea, mainly in the Second Division. In August 1983 he moved to newly promoted Queens Park Rangers, managed by Terry Venables for £155,000, helping them to establish themselves as a top flight side.
He was released in the summer of 1987, having scored 9 times in 97 games for Rangers, joining Portsmouth in July 1987. Portsmouth had just been promoted to the top flight for the first time in nearly 30 years, but it lasted just one season and Fillery found himself playing Second Division football once more.
In October 1990 he moved to Oldham Athletic, but couldn't establish himself, joining Millwall on loan on the 28th of March 1991. At the beginning of the following season he found himself out in the cold at Oldham as the Latics embarked on top flight football. He joined Torquay United on loan in September 1991, playing four league games which turned out to be his last games in the Football League.
He later joined Crawley Town and was their assistant manager until August 1994. In January 2000 he was linked with the manager's post at non-league Southall, the plan being that he would be joint-manager with his former teammate Terry Fenwick, who was at the time Southall's Director of Football. However, this plan backfired when the chairman who had set up the deal was reported to have been sacked by the club's backers for not consulting them first.
He later returned to Chelsea as a coach at the club's Youth Academy.