Mary Kay Cabot of Cleveland.com initially reported the news.
The standout offensive tackle spoke about his decision in the team's press release:
"This was an extremely difficult decision, but the right one for me and my family. Playing in the NFL has taken a toll on my body and I can no longer physically compete at the level I need to.
"From the moment I was drafted, the city embraced me in a way that I could never fully describe. I am proud to call Cleveland home. The loyalty and passion of the fans is unmatched and it was an honor to play in front of them from the past 11 years. I would like to thank all of the coaches, teammates, staff, fans and everyone who has shown me support throughout my career. Even though I will be hanging up my cleats, I will always be a Cleveland Brown."
Cleveland Cavaliers superstar LeBron James paid his respects to Thomas via Twitter:
Many things have gone wrong for the Browns since they returned to the NFL 19 years ago, but Thomas was one of their bright spots after they drafted him No. 3 overall in 2007.
Thomas became an immediate starter at left tackle for the Browns as a rookie. He had two historic streaks come to an end in 2017 when he suffered a torn triceps during an Oct. 22 game against the Tennessee Titans.
In addition to Thomas' string of consecutive snaps, his 167 consecutive regular-season starts were the fourth-most among active NFL players behind New York Giants quarterback Eli Manning (210), Los Angeles Chargers quarterback Philip Rivers (192) and Dallas Cowboys tight end Jason Witten (179). Manning's streak likewise came to an end in 2017.
When Thomas first gave indications he was thinking of retirement, the 33-year-old wanted to make sure he gave the Browns notice before the start of free agency so they could plan accordingly.
"Obviously, they want to know before the draft and free agency, so that if they have make different plans if I'm not going to be there, they want to know about it," he said at the Greater Cleveland Sports Awards banquet in January. "I told them I'll make a decision when I'm ready and let them know and give them as much time as I possibly can."
Per ESPN Cleveland's Tony Grossi, Thomas said on March 6 he has auditioned for jobs in television as a football analyst.
With his playing career now over, Thomas likely will end up in the Pro Football Hall of Fame when he becomes eligible in five years. He was a model of consistency throughout his career, was named to 10 straight Pro Bowls from 2007-16 and was named to the All-Pro first or second team nine times in 11 seasons.