The midfielder had been serving a six-month sentence for beating up a 16-year old back in December.
Wearing jeans and a jumper and carrying a holdall, the 25-year-old, was freed from Manchester's Strangeways jail.
Should Barton Get The Boot? You Tell Us!
Kevin Keegan said the £5.8m man should be welcomed back by the club.
Keegan said: "People have opinions, and you must respect those, but mine is to give him another chance."
SHOULD NEWCASTLE KEEP HIM OR SHOW HIM THE DOOR?
E-MAIL US AND WE WILL PUBLISH YOUR COMMENTS TOMORROW.
Contact us - Kevnumad@fsmail.net
Barton was locked up on May 20 after pleading guilty to assault and affray at Liverpool Crown Court. The charges related to an incident last December in the city.
The court heard the midfielder, then out of the Newcastle team through injury, had been on a night out in his home city with friends.
After drinking 10 pints and five bottles of lager, the group went into McDonald's at about 5am on December 27. Barton became involved in a row with some youths.
CCTV caught Barton straddling his victim, punching him up to 20 times. Moments later the player attacked 16-year-old Jordan Spencer, punching him in the belief the youth had assaulted his cousin.
Barton was released on electronic tag, having served less than half of the six-month sentence. The midfielder gave no comment to assembled reporters.
He is still subject to a suspended sentence, relating to an attack on ex-team-mate Ousmane Dabo, who was left unconscious after a training ground bust-up.