The 22-year-old will spend the rest of the season at Elland Road, which could be turned into a long term deal at any time with Leeds having agreed an exclusive option to buy.
Olembe made his international debut for Cameroon against Cuba when he was still only 16, and a year later played for the Indominatable Lions in the World Cup finals at France '98.
He played three games in last year's World Cup finals in Japan and South Korea, and has already 56 caps, scoring six times for his country.
Peter Reid is delighted to have been able to bring him to the club, and says he will offer him options that have so far been lacking in the United squad.
"He's one of those players in the middle of the park who can handle the football with quick feet and can get about," said Reid to the official Leeds website.
"If we get a few injuries or suspensions we're down to the bare bones and it's another body in there and in certain games where I want to change the formation he's one of the players you look to in that situation.
"I've seen him once or twice and he is a really good player."
Olembe has spent all his professional career in France, starting out as a 17-year-old with Nantes, helping them to the French title in 2000/01.
He joined former French champions Marseille for the start of the 2001/2002 campaign.
Last season he played 28 times for Marseille, scoring just the once.