The 30-year-old joins the City Ground club for a four-week spell and is expected to go into Saturday's squad for their home relegation encounter with fellow strugglers Bradford City.
The England international completed the formalities of his temporary move on Friday morning and his addition is seen as a key boost to Kinnear, with Forest desperate to pull themselves out of trouble at the foot of the Division One table.
"I'm delighted to have a player of Nicky's quality on board with us. He has got a great pedigree and he's enthusiastic to play for Nottingham Forest," Kinnear told the club's official website.
"He has played for some great clubs and his record of international appearances speaks for itself - as does the fact that he has been involved in transfer deals totalling almost £20 million.
"Nicky has been in the first team set-up at Leeds just recently and I've also seen him play for their reserve side. He's in great shape and really keen to make an impression."
