He made his first-class debut in 1996 against Lancashire at Cardiff taking 6 wickets in the match.
In 1997 he was given a longer run in the Glamorgan side as Robert Croft was playing for England.
Cosker won his county cap in 2000 and became a key member of Glamorgan's highly successful one-day team between 2000 and 2005, where his accurate bowling, often in tandem with Robert Croft, and fielding backward of square on the off side were key to Glamorgan's success.
In September 2013, as new contract negotiations stalled, Cosker claimed his 500th first-class wicket for Glamorgan.
[2] as of 18 August 2016 This biographical article related to an English cricketer born in the 1970s is a stub.