The 28-year-old, who arrived on Tyneside in July 2007 for around €6.5 million from Manchester City, has been told that he can leave St James' Park on a free transfer after a number of cryptic statements made on Twitter criticising the club's hierarchy.
The midfielder was an integral part of the Newcastle side that won the Championship under Chris Hughton in 2009-10, and played a key role in keeping the side in the Premier League last season, despite the upheaval at the club that followed Hughton's dismissal and the subsequent arrival of Alan Pardew.
Barton was runner-up in the fans' player of the year vote, whilst the team failed to win a single league match when Barton was unavailable.
A statement on the club's official website has announced that the once-capped England midfielder can leave.
"Newcastle United can confirm that Joey Barton has been placed on the transfer list on Monday," said the club statement.
"The player has been advised that he can leave the club on a free transfer."
Barton has since said, via his Twitter account: "Somewhere in those high echelons of NUFC they have decided I am persona non grata.
"I am on a free but the honour of wearing those black and white stripes surpasses that."
He added: "One day the board might realise what the shirt signifies. HONOUR and PRIDE. Thanks for your continued support........... #toonarmy"