 After helping the club remained in the Championship, Mellis finished his first full season at Barnsley, scoring six goals in thirty-six appearance.In the 2013–14 season, Mellis continued to be in the first team, though he suffered injuries.Mellis scored his first Barnsley goal of the 2013–14 season on 3 December 2013, in a 2–1 win over Brighton & Hove Albion.