"Luca Toni asked the board of Bayern Munich in personal talks to lend him to AS Roma until the end of the season for personal reasons," Bayern said in a statement.
"He wants to realise his biggest aim, playing for Italy in the 2010 World Cup in South Africa, with regular appearances in Serie A."
The 32-year-old's move comes as little surprise, with the Italian saying publicly on numerous occasions that he wanted to leave Bayern following a breakdown in relations with Bayern's Dutch trainer Louis van Gaal.
Signed from Italian side Fiorentina in 2007, Toni was the Bundesliga's top scorer in his first season, with 24 goals in 31 league games on the way to Bayern winning the German title.
But since van Gaal's arrival on July 1, he has made just four league appearances, and has failed to score all season.
He stormed out of Bayern's 1-1 draw with Schalke 04 in the Bundesliga on November 7 after the coach replaced him at half-time and the Italian was later fined for his conduct and apologised.
"The Bayern Munich board thanked Luca Toni ... and wished him all the best at AS Roma, lots of success and above all a place in the World Cup," it said.
The Bayern Munich president meanwhile denied on Thursday press reports that the German giants' French international Franck Ribery was going to move to Real Madrid in a €55 million deal next summer.
"There are no offers at the moment, no options and no talks at all either about him or with him," Uli Hoeneß told the Süddeutsche Zeitung daily.
German specialist website ran.de had reported on Wednesday that the 26-year-old winger's move was hammered out in August between Bayern and the Spanish club at the time of Dutch star Arjen Robben's transfer to Munich.
Bayern did not pay Real the agreed €25 million price tag for the Dutch winger, instead sitting on the cash in anticipation of the Ribery deal, said ran.de, which is owned by German private broadcaster Sat.1.
But Hoeneß, club manager at Bayern for 30 years who replaced Germany legend Franz Beckenbauer as president in November, said this was wide of the mark. "There is no deal with Real. We paid for Robben quite normally," he said.
He also said that the club wanted Ribery to stay once his contract expires in 2011: "That is our first option. Only if we see no chance of this will we start talking to other clubs."
Ribery, who has been out of action through injury for over two months, has made no secret in the past of his desire to join Real.