In an interview with CNN, Giuliani said he wanted to clarify that his role in the legal department would be "limited".
Giuliani told CNN that he would turn to Special Adviser Robert Mueller during his Russia investigation and help to bring it to an end by saying that it "needs a bit of pressure".
Müller examines Russia's involvement in the 2016 elections, including possible ties between the Trump campaign and Russia. Trump has repeatedly denied any agreement.
Giuliani, who had telephoned CNN shortly after hearing CNN's phone call, was keen to praise Trump's current legal department, but he said that sometimes it helps to create a new perspective.
Giuliani has noticed that too He has known Müller for a long time. They worked together in the Ministry of Justice when Müller was FBI director and Giuliani was New York's mayor.
Giuliani said he'll get a list of Mueller's what it takes to do the rest of the investigation as soon as he can, and depending on what's on the list, compliance could go quickly, even after "one." a few weeks".
Giuliani dismissed the idea that Trump ever intended to dismiss Muller. He said the president had never given him any indication that he was considering such a move because he knew it was "counterproductive." The dismissal of Mueller would mean that the investigation would take longer, said Giuliani, adding that "Bob is the best we can do" and said that he is fair.
Trump's attorney team struggled to find lawyers willing to support the President of the Russia probe.
A well-known source said that part of the reason for Giuliani joining the team was the departure of Dowd.
"John Dowd left abruptly and put Sekulov in a hole, he needs employees," the source said.
Giuliani's law firm Greenberg Sad announced on Thursday that he would bid farewell.
"Mr Giuliani is now taking leave of absence for an indefinite period of time to deal with matters that have nothing to do with the firm or its client," states a statement by Richard A. Rosenbaum, the chairman of the firm ,
Giuliani was a prominent supporter of Trump's presidential bid and, according to two sources, Giuliani was at the President's Resort in Mar-a-Lago this week. One source said Trump and Giuliani had a 30-minute interaction while they were there.
"I announce today that former New York City Mayor and US attorney for the Southern District of New York, Rudy Giuliani will join the personal staff of the President's team," Sekulov said in a statement, adding that Trump said that Giuliani was "great" and had been his friend for a long time.
Sekulov's statement said, in a statement, Giuliani said, "It is an honor, an I am looking forward to cooperating not only with the President, but also with Jay, Ty and their colleagues," a nod to White's Special Adviser House, Ty Cobb.
Sekulow announced two more additions to Giuliani ̵
The Raskins do not comment on joining the Trump team.
CNN's Katelyn Polantz, Jim Acosta, Kara Scannell, Elizabeth Landers, Kevin Liptak and Jeff Zeleny have contributed to this report.