"I'm just so happy to be able to play basketball again, no matter what my role is," Marbury said, wearing a Celtics warmup before his No. 8 jersey was rushed over for a photo opportunity.
"I was lit up because the tradition of the Celtics - you think about the championships, you think about all the guys who have played here. The history speaks for itself."
Marbury, who turned 32 last week, hasn't played a regular-season game in more than a year while fighting with Knicks management over his role and, ultimately, a buyout of his $20.8 million contract.
The former All-Star, who alienated Knicks management, teammates and fans, was waived on Tuesday after he agreed to a settlement.
"I'm human. I make mistakes," Marbury said. "I have learned from my mistakes. You've got to keep on pushing on."
Coach Doc Rivers said he wasn't concerned about introducing a potential malcontent into what has been a harmonious locker room, a domain kept in check by veteran All-Stars like Paul Pierce, Kevin Garnett and Ray Allen.
"That was New York, and everywhere else. That has nothing to do with today," Rivers said. "We're doing very well. Our locker room's pretty strong."
The Celtics were expected to pay Marbury a pro-rated share of the veteran's $1.3 million minimum.
Marbury was the center of controversy during his five years in New York, feuding with coaches and skipping games. He took a long leave of absence when his father died in December 2007, followed by season-ending ankle surgery; he has not played since Jan. 11, 2008.
Marbury returned to the Knicks in training camp, but when offered a buyout he refused to surrender any more than $1 million of his salary. Coach Mike D'Antoni told him to stay home.
"I never hesitated as far as my decision as far as going forward with the Knicks," Marbury said. "I was prepared to play or not play."
Both sides dug in until this week, when they reached a settlement that left Marbury free to sign with a contender in time to be eligible for the postseason.
"He's a talented player, obviously, and Boston is a very talented team," D'Antoni said. "You never know, but again, a guy that talented coming off the bench, it's not a bad chance to take."
The Celtics were in need of another guard because of an injury to Tony Allen and the two-game suspension of Gabe Pruitt, who was arrested early Thursday morning on suspicion of drunken driving.
Eddie House, who has been backing up Rajon Rondo at point guard, is more of a shooter.
The situation mirrors the one last year, when the Celtics signed Sam Cassell midseason and he helped bolster their roster. Cassell, who was traded this month without appearing in a game this season, took weeks last year to make his way onto the floor, but Marbury will be thrown right into the rotation.
"We're just going to throw him out there," Rivers said. "It's impossible for him to mess up a play tonight. One of the things I told Steph is just to be free, to just play" Rondo said he was glad to have Marbury aboard, saying: "He's a veteran, so he can only help."
Marbury cleared waivers at 10 a.m. and arrived at the Celtics practice facility in Waltham for his physical before noon. He could be seen from the public area of the workout facility wearing a white, long-sleeved T-shirt and sweat pants, jumping up and down as he took the practice court, smiling and chest-bumping with several people wearing Celtics gear.
After few minutes, the automatic shades were lowered.
"We are very excited to have a player of Stephon's caliber joining our team," Celtics general manager Danny Ainge said. "Our entire organization is confident in the belief that Stephon can play an important role in helping us to win another championship."
Marbury, who also played with Garnett in Minnesota, said he received a warm welcome.
"Everybody was excited, which I was happy about," he said.
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