A second-round pick in 2010 out of Penn State, Lee was a two-time Pro Bowl selection (2015, 2016) and the unquestioned leader of the defense for most of his career.
"It's been a complete honor," Lee told ESPN. "I've been blessed to play for the incredible Jones family, with such great coaches and teammates that I love like brothers. I loved every minute playing and tried to pour my heart and soul into winning and helping my teammates at all costs.
"To say the injuries were frustrating would be an understatement, but the support I received through them all was humbling and the lessons I learned battling adversity will last a lifetime. There are always regrets, but I'm proud of what I was able to accomplish and I leave this game grateful."
Injuries marked Lee's time with the Cowboys, but when healthy he was one of the best linebackers in the NFL. The 34-year-old led the Cowboys in tackles in 2011 and 2015-17, and he owns five of the top seven tackle games in team history, including a record 22 vs. the Giants in 2016. He also had 14 career interceptions, returning two of them for touchdowns; 5 fumble recoveries; 2 forced fumbles; 59 tackles for loss; and 4 sacks.
He was credited with 995 tackles for his career, good for eighth in team history. He averaged 8.4 tackles per game, the most among the top 10 tacklers in team history. Darren Woodson, who is the franchise leader with 1,350, averaged 7.6 tackles per game.
Lee missed time with hamstring, wrist, toe, neck, knee and core-muscle injuries as well as concussions. He missed the 2014 season because of a torn anterior cruciate ligament. He played in just nine games last season after undergoing sports hernia surgery in September but was feeling better at the end of the year and contemplated a return for a 12th season.
His impact off the field was just as great as it was on the field.
"As an individual he's one of the most selfless people that I've ever been around," linebacker Leighton Vander Esch said after the season. "The dude just truly loves the game, and he is going to do what's best for the game. He's extremely intelligent, he understands it like nobody I've been around. He's just a phenomenal individual -- his character bleeds off and is contagious.
"He's like an older brother to me, and I know he wants to see everyone around him succeed and that's just what's special about him. If other people are succeeding, [if] the team is succeeding? He's just as happy as if he was out there doing it. I think it's special to have a guy like him around. They don't come around very often."
Lee's decision continues an offseason shift for the Cowboys in longevity and leadership as defensive lineman Tyrone Crawford, a nine-year veteran, also elected to retire and the team moved on from 16-year long-snapper L.P. Ladouceur.
With Lee and Crawford not returning, DeMarcus Lawrence, a second-round pick in 2014, is the longest-tenured defensive player on the Cowboys. Randy Gregory, a second-rounder the next year, is the second.