Perfectly set up by his lead-out man Mark Renshaw, the Briton surged with 200 meters to go before the finish line in Montpellier to easily beat American Tyler Farrar and Italian Alessandro Petacchi.
The win, his 19th overall in the Tour de France, strengthened the Manxman's top spot in the race for the green jersey.
In the points classification, Cavendish now leads Spaniard Jose Joaquin Rojas by 37 points and Belgian champion Philippe Gilbert by 71 points before the second rest day in this Tour.
The overall leader's yellow jersey remained on the back of Frenchman Thomas Voeckler, who finished within the main pack.
Voeckler leads Luxembourg's Frank Schleck by one minute and 49 seconds with Australian Cadel Evans third 2:06 behind.
The long ride along windy roads from Limoux included a long breakaway involving Dutchman Niki Terpstra, Russian Mikhail Ignatyev and Frenchmen Samuel Dumoulin, Mickael Delage and Anthony Delaplace.
The last of the escapees, Terpstra, was caught two kilometers from the line.

Meanwhile, Alexandre Vinokourov has announced his retirement from cycling a week after breaking his right femur in a crash on the Tour de France.
The 37-year-old Kazakh star told French television on Sunday that "I will stop there" and that he is looking for a new role within the Astana team. He was due to retire at the end of the season.
Vinokourov was one of about 30 riders caught up in a pileup midway through the Tour's ninth stage. The Astana team leader flew off his bike and had to be helped up by teammates.
He was flown to Paris to undergo surgery.
Vinokourov, who was third at the 2003 Tour, served a two-year doping suspension after twice testing positive for banned blood transfusions during the 2007 race.