Defender Jim McNulty and Barnsley have agreed a mutual termination of his contract.
The 28-year-old joined from Brighton and Hove Albion in 2011 and won Players' Player of the Year in his first season.
He struggled with injury last season and made just 15 appearances then was still given a new one-year contract by manager David Flitcroft but his only appearance since then came in the 5-1 League Cup loss to Southampton and he has spent most of the season on loan at Tranmere Rovers in League One.
He is the third player to be released by Barnsley this month after Chris Dagnall, who has now joined Leyton Orient, and Scott Wiseman who is now at Preston North End.
