On 7 July 2009, Wellens joined Leicester City for a potential fee of £1.2m, signing a three-year contract. Their biggest signing of the summer, Wellens was named by the BBC Sport as the club's key player for the 2009–10 season. He made his debut in a 2–1 win over Swansea City on 8 August 2009, scoring his first goal in a 2–0 win over Middlesbrough on 2 May 2010. Wellens featured in all but three matches for Leicester in the Championship that season. He played a crucial role in Nigel Pearson's team that reached the play-offs semi-finals, where they lost to Cardiff City on penalties.