 Mellis scored his first goal for Barnsley during a 1–0 win over Bristol City on 1 September 2012, followed scoring his second goal three weeks later on 18 September 2012, in a 2–1 loss against Blackburn Rovers.The following game against Birmingham City on 22 September 2012, Mellis provided a hat-trick assist, in a 5–0 win.Two months later on 24 November 2012, Mellis' fourth goal came in a 2–1 win over Cardiff City.