West Ham capture Keane on loan
"I like him as a player but he's also a good character which we need, he's an intelligent player and one who can score goals," West Ham manager Avram Grant told Sky Sports.
Keane, who has also played for Inter Milan, Celtic and Leeds United in a much-travelled career, said: "I'm just happy to get back playing football again, it's frustrating sitting on the bench.
"It's a fantastic club with great tradition. They're not in the best position at the moment but I'm hopefully here to help the squad.
"If you look at how close it is you get a couple of results you move swiftly up the table."
Spurs also released wide man Jamie O'Hara, who has not played all season because of a back injury, on loan to Wolverhampton Wanderers on Sunday.