The St James' Park management regard Barton as a disruptive influence in the dressing room due to his recent behaviour, and will let him leave with a year left on his contract.
Pack your bag: Joey Barton has been offered a free transfer from Newcastle
In a brief statement on their website, the club said: 'Newcastle United can confirm that Joey Barton has been placed on the transfer list today.
'The player has been advised that he can leave the club on a free transfer.'
A host of Premier League clubs will be keen to take Barton with Manchester United and Liverpool known to be interested.
The player had taken to Twitter earlier on Monday to reveal that a major announcement on his future would be made at 4pm.
And eventually at 4.55pm he tweeted: 'Somewhere in those high echelons of NUFC, they have decided, I am persona non grata.
Feisty: Barton is regarded as a disruptive influence and will be allowed to leave
'I am on a free but the honour of wearing those B+W stripes, surpasses that.
'One day the board might realise, what the shirt signifies. HONOUR and PRIDE. Thanks for your continued support. #toonarmy'.
Barton launched an attack on the Magpies following the weekend defeat at Leeds, using his Twitter accountto defend team-mate Jose Enrique after the full-back was fined for accusing the club of lacking ambition.
Barton said, following the 3-2 loss at Elland Road: 'If only we as players could tell the fans exactly how it is, without them above fining us lots of money. There will be a time and a place.
Had enough: Alan Pardew doesn't want Barton around the club
'If it wouldn't effect team morale and cause unrest within the dressing room, am certain Jose's comments would be the tip of the iceberg.'
He added: 'Things need addressing as am not prepared to go through a relegation again.'
Judging by their efforts, Newcastle need to improve before they face Arsenal at home a week on Sunday.
Barton joined Newcastle in 2007 from Manchester City in a deal worth ?5.8million, and was one of Sam Allardyce's first signings.
He has gradually grown into his own on Tyneside and after excelling last season in a variety of roles, was many of the fans choices to succeed Kevin Nolan, who has joined West Ham, as captain.
His bad reputation and murky past, though, are never far away and earlier this summer he was unable to join the club on their US tour after being denied a visa to visit the country.
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