Sidwell joined Chelsea on 1 July 2007 on a free transfer from Reading, and was given squad number 9 for the 2007–08 season. In his first interview after joining Chelsea, Sidwell stated that he had not come to Chelsea to 'make up the numbers', and that he believed training and playing alongside top players like Michael Essien and Frank Lampard would only help him improve. After playing in the club's pre-season tour of the United States, Sidwell then played in the 2007 FA Community Shield where Chelsea lost on penalties to Manchester United. His league debut for Chelsea came on 12 August 2007 in a 3–2 victory against Birmingham City when he replaced Florent Malouda in the 83rd minute.