His club career was then rejuvenated under new manager Tony Mowbray, becoming a first team regular again, and put in several man of the match performances during 2006–07. He won the Powerade Championship player of the month award for December 2006. Koumas was named the Championship Player of the Year at the Football League Awards in March 2007, and was also honoured in April with a place in the Championship team of the year.
In July 2007, West Brom agreed a fee of £5.3 million with Wigan Athletic, stating that it was a head-turning offer. Koumas completed the move to Wigan on 10 July. Tranmere received a portion of the transfer fee having previously included a sell-on clause in their agreement with West Brom. He made his Wigan debut on 11 August 2007 in a 2–1 defeat away at Everton. The following month he marked his 300th career league appearance by scoring his first goal for his new club, converting an 80th-minute penalty to rescue a 1–1 home draw with Fulham. Due to injury and a lack of first team opportunities under three different managers during his three years at Wigan, Koumas was linked with a return to previous club West Bromwich Albion along with Newcastle United and Leicester City on a loan deal until the end of the 2009–10 season, however a loan move never materialised. Koumas was released at the end of 2010–11 season following his return from a loan period at Cardiff City.