The couple, who have been dating since 2011, wed in front of about 10 people in Mazan, Provence - close to where the bride's family has a holiday home.
Mayor Aime Navello told the Associated Press he married them at the town hall.
The short service was followed by a reception for family and friends, reported to have included Righton's bandmates and actress Sienna Miller.
Knightley, 28, announced her engagement to Righton, 29, last year.
"Keira was a charming bride, very modest and simple in her attitude, as was James," Mr Navello told the Daily Mail.
"I got the impression that it was a very moving experience for both of them."
The actress, who was Oscar-nominated for her performance in 2005's Pride and Prejudice, is the daughter of playwright Sharman Macdonald and actor Will Knightley.
She rose to fame in the British hit Bend it like Beckham, becoming an international star in films including Love Actually and the Pirates of the Caribbean franchise.
'More interesting'
Knightley also won critical acclaim for her performances in films such as Atonement, A Dangerous Method and, most recently, Anna Karenina.
Later this year, she will be seen in Jack Ryan - a prequel to previous Tom Clancy adaptations - playing Cathy Ryan opposite Chris Pine.
Singer and keyboard player Righton has performed with indie rock band the Klaxons since 2005. The group won a Mercury Music Prize in 2007 for their debut album Myths Of The Near Future.
In an interview last month, Knightley said she did not want an extravagant wedding day.
"We're not 'big wedding' types. I don't need to have all that. I'm just trying to enjoy the engagement bit.
"My parents are together after 40 years. The fights are there but they love each other.
"It's not like the first three months, the first two years... whatever it is, but I think it gets more interesting, or I hope so."
Actress Keira Knightley has married Klaxons star James Righton in the south of France.