In a surprise move, Magpies officials have placed Barton on the transfer list after he launched a series of Twitter rants at the club's hierarchy.
Barton can now leave St James' on a free transfer, with a number of Premier League clubs expected to be interested in securing his services.
A Newcastle United statement released this afternoon said: "Newcastle United can confirm that Joey Barton has been placed on the transfer list today (Monday).
"The player has been advised that he can leave the club on a free transfer."
Earlier this morning, Barton had promised to make an announcement on his future on Twitter at 4pm.
The Liverpudlian yesterday Tweeted a series of cryptic messages hinting at problems behind the scenes at St James'.
Barton said yesterday: "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."
He referred to team-mate Jose Enrique's recent fine for critical Tweeting after the Spaniard accused the club of lacking ambition when he added: "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.
"And again it would be left to those magnificent fans to pick up the remnants of their once great football club. #hadenoughofcertainpeople.
"If I wanted to leave, I'd just come out and say I want to leave. Things need addressing as am not prepared to go through a relegation again."
This afternoon he added: "I won't be commenting on situation at Newcastle again, as I feel it helps nobody and serves no purpose. Hope u all understand, only to add barely 30 minutes later: "I will be making an announcement regarding my future, on here at 4pm today"
Barton has a year left on his Newcastle contract but claimed recently he had no interest in a move elsewhere.