Former New York City Mayor Rudolph Giuliani will neither run for governor nor for the U.S. Senate, Republican sources have told NY1.

Instead, Giuliani is set to endorse Republican Rick Lazio, a former congressman from Long Island, for governor at an event in Midtown this afternoon.

Giuliani has decided to focus more on his business, said a Republican source on Monday. In particular, said the source, Giuliani is committed to his law firm and to Giuliani Partners, which just received a contract for the Rio de Janiero Olympics.

According to the source, Giuliani is "still committed to strengthening the Republican Party and will be working on trying to broaden its base."

The source added that Giuliani has enjoyed being a surrogate and likes campaigning for other Republican candidates and will continue to do so.

Political observers say Giuliani's decision not to run highlights how few stars the state Republican Party has to choose from. At the moment, only Lazio has declared his candidacy for governor. Erie County Executive Chris Collins has also been rumored to want the state's top job.

Giuliani's move could embolden Governor David Paterson, who is polling well against Lazio. Paterson's low approval ratings have prompted many in the Democratic Party, including the Obama administration, to push for Paterson to step aside and let State Attorney General Andrew Cuomo run for governor.

“The Republican Party statewide has been in a little bit of trouble for a number of years,” said David Birdsell, dean of Public Affairs at Baruch College. “Their great opportunity is Governor Paterson's weakness, and whether they can capitalize on that with a candidate that has a message, is a great campaigner, that's an open question.”

Giuliani's endorsement will also put an end to speculation about Giuliani's future and may effectively end his political career.

“The question is, what is the second act at this stage? And it is not clear if there is a plausible second act,” said Birdsell.

Giuliani ran for president in 2008 in a campaign, where he won only one Republican delegate and racked up $3.6 million in debt, which he has yet to pay off.

In 2000, Giuliani dropped out the U.S. Senate race after being diagnosed with prostate cancer. Lazio ran and lost to now-Secretary of State Hillary Clinton.