Former New York City mayor and U.S. attorney Rudy Giuliani is vowing to bring to an end Robert Mueller's longrunning Russia investigation as he joins President Trump's legal team, touting his personal relationship with the special counsel.

Whether Giuliani will be a gamechanger for the president's ever-changing legal lineup and the ever-expanding probe remains to be seen. But he voiced confidence as the news broke he'd been hired.

It shouldn’t take more than “a week or two” to come to a resolution on the probe, Giuliani said.

“I’m going to join the legal team to try to bring this to a resolution,” Giuliani told The New York Post. “The country deserves it. I’ve got a great admiration for President Trump.”

Giuliani announced Thursday that he would join Jay Sekulow and White House liaison Ty Cobb on Trump's team, amid the probe of Russian meddling and potential collusion with Trump team associates in the 2016 election.

Giuliani was a surrogate for the president during his 2016 presidential campaign. The two have been close friends for years.

The former New York City mayor said Thursday he hoped to “negotiate an end” to the investigation with Mueller.

“I’ve had a long relationship with Bob Mueller. I have great respect for him. He’s done a good job,” Giuliani told The Post. Giuliani served as mayor of New York City while Mueller headed the FBI. “I don’t know yet what’s outstanding. But I don’t think it’s going to take more than a week or two to get a resolution. They’re almost there.”

He vowed to ask Mueller what he would need to “wrap it up,” but also told The Washington Post on Thursday that Mueller “should be allowed to do his job, he’s entitled to do his job.”

Giuliani was mayor of New York City from 1994 to 2001 and served as U.S. attorney for the Southern District of New York from 1983 to 1999.

“The President said, ‘Rudy is great. He has been my friend for a long time and wants to get this matter quickly resolved for the good of the country,” Sekulow told Fox News in a statement Thursday. “I have had the privilege of working with Mayor Giuliani for many years, and we welcome his expertise.”

Sekulow added that Giuliani “expressed his deep appreciation to the President for allowing him to assist in this important matter.”

A source with knowledge of the situation told Fox News that Giuliani made the decision to join Trump’s legal team in the past few days, following a dinner with the president earlier this month at Trump’s Mar-a-Lago resort.

The addition of Giuliani to Trump’s outside legal team comes after a tumultuous time for the unit. Last month, Trump's lead attorney John Dowd resigned, following Dowd’s strong opposition to the president doing an interview with Mueller.

Trump has said he would “like to” interview with Mueller. But it is unclear whether the president might still consider an interview with the special counsel, especially after the raid on his longtime attorney Michael Cohen's properties.

A source said Thursday, though, that Deputy Attorney General Rod Rosenstein told Trump last week that the president is not a target in the Cohen investigation, and that the investigation is focused solely on Cohen.

Trump has been told previously that he is not a target of Mueller's investigation.

Also last month, former U.S. attorney Joseph diGenova and his wife and law partner Victoria Toensing joined the president’s legal team. However, due to “conflicts of interest,” the team withdrew from defending Trump in the Russia probe.

Fox News' Matt Richardson and John Roberts contributed to this report.