The 26-year-old has signed a three-year contract and becomes manager Guy Luzon's latest addition at The Valley.
Kashi made 86 appearances and scored once during his three-year stay at the French club.
CONFIRMED | Ahmed Kashi has put pen to paper to make his move to The Valley official. #WelcomeAhmed#cafcpic.twitter.com/y2fpDLmxPL
— Charlton Athletic FC (@CAFCofficial) July 21, 2015