After being told he can leave Huddersfield Town in the January transfer window, it was announced on 9 January 2015, he joined fellow Championship side Rotherham United on loan for the rest of the season. Hammill made his Rotherham United debut the next day, playing the whole 90 minutes, in a 1–0 loss against Brentford. Despite missing some games due to being ineligibile to face his parent club, Hammill helped the club survive relegation and made fourteen appearance for the club. Hammill returned to his parent club after Rotherham United made it clear to Hammill that they would not sign him on a permanent basis.