The 29-year-old joined in an initial loan deal until the end of the season, with the option of a permanent deal in the summer, and moved to United a day after Cameron Stewart arrived from Hull.
The Mali winger has played in the Premier League for both Reading and Crystal Palace, is well-known to Leeds manager Brian McDermott and was part of his promotion-winning squad at the Madejski Stadium in 2012.
McDermott said: "Jimmy is a player that I scouted from France in 2006. He has fantastic pace, he is a real team player, and he made and scored goals for us in the Championship and the Premier League.
"I'm delighted he's come on board and I'm really looking forward to working with him again."
Kebe, who started his career in France and had spells with Lens, Chateauroux, and Boulogne, made almost 200 appearances for the Royals before making the move to Palace last summer.
However, he made only six appearances for the Selhurst Park club after transferring for an undisclosed fee in August.
Leeds chairman Salah Nooruddin said: "Jimmy Kebe is a player well known to Brian and we're delighted to have agreed a deal both with the player and Crystal Palace."