The 23 year Mali international joined the Royals from Lens last January.
Director of Football Nick Hammond said: "Jimmy has now found his feet with us and adjusted well to English football, illustrated by the fact he already has seven assists this season.
"He's an exciting talent who gets supporters onto the edge of their seats and it's very important we have secured him for the next three-and-a-half years because he's the kind of player who is bound to create interest from other clubs."
Kebe added: "I'm very pleased to sign this new contract. I am happy at Reading, playing in a good team and I hope we will get promotion to the Premier League at the end of the season."