Agent Jim Steiner said Green was proud of a career that included a Super Bowl ring with the Rams and two Pro Bowl appearances with Kansas City, but was ready to get onto the next phase of his life.
"He thinks it's the right time," Steiner said Friday. "He had a long, prosperous, very successful career. He believes he can still play, but the demand isn't real high out there right now and he's not the type of guy who's going to sit around for four or five months waiting for the phone to ring."
Green, an eighth-round draft pick by San Diego in 1993, was released by St. Louis in February after playing three games in his second stint with the Rams last season.
Green, 38, earned a Super Bowl ring in his first go-round with the Rams in 2000, but had to watch Kurt Warner lead the Rams to their first title after injuring his knee in a preseason game.
His best years were in Kansas City from 2001-06, when Green earned two trips to the Pro Bowl (2003, 2005) and threw for more than 4,000 yards in three straight seasons.
Dick Vermeil, who coached Green with the Chiefs, said Green called him Friday morning to let him know of his decision.
"For three years in a row, Trent had a 90 quarterback efficiency rating," Vermeil said from his home in Pennsylvania. "He was the only quarterback in the league who did that at that time. I don't know what more you can ask a guy to do. Very few did it better than him during the five years he was with the Chiefs."
