French rider Thomas Voeckler kept the race leader's yellow jersey after the 104.1-mile trek from Blaye-les-Mines to Lavaur. Voeckler finished 75th in the stage but with the same time as the winner.
However, Voeckler said he was expecting to lose his yellow jersey during today's 12th stage.
Cavendish made the most of the last stage designed for sprinters before the race reaches the Pyrenees to claim his 18th stage win at the Tour, his third in this year's race. He won in 3 hours, 46 minutes, 7 seconds.
"It's incredible to have the green jersey. It's the most beautiful jersey in the world," said Cavendish, who got an assist from HTC-Highroad teammate Mark Renshaw.
Cavendish's efforts were almost ruined toward the end when he hit the front wheel of Frenchman Romain Feillu's bike.
"There were 10 of us close together and my shoe banged into his front wheel," he said. "My foot technically came out of the shoe -- I had to reach down and slide the ratchet and redo it with 600 meters to go. I was lucky there were no swerves in the peloton. It could have been quite dangerous."
HTC-Highroad manager Bob Stapleton said intermediate sprints tired out Cavendish this year after race organizers changed the rules. There is only one intermediate sprint in each stage, with 20 points available to the rider who wins -- as opposed to six points in previous years when there were more intermediate sprints.