Wall Street Journal: In an interview, Mr. Giuliani, a former US attorney for the Southern District of NY, said his first task after joining the team will be to "find out what Bob Mueller needs" to complete the investigation.
"Rudy is great", Trump said in the statement issued by Sekulow. "He has been my friend for a long time and wants to get this matter quickly resolved for the good of the country, '" Sekulow, said according to Newsday.
Other lawyers joining the president's personal defense team include Jane Serene Raskin and Marty Raskin.
"He knows Bob Mueller, he's very fond of the president, and I think this is a great thing for the president and more so the country - and I think that's one of the reasons Rudy's doing this", Kerik said.
He also worked with Mueller when he was director of the Federal Bureau of Investigation and Giuliani was New York's mayor.
Giuliani added he's been speaking with PEETUS for weeks about joining the group of legal advisers, which has been struggling to recruit new members following the raid of Michael Cohen's records and all that Stormy Daniels drama.
Earlier that year he had left the firm he founded, Bracewell & Giuliani, to join Greenberg as global chair of its cybersecurity and crisis management practice. He praised the team and said sometimes a fresh perspective helps.
Trump's legal team had been short-staffed for several weeks, since the departure of attorney John Dowd last month.
The former presidential candidate told CNN his role will be "limited", adding that his focus will be on giving the Russian Federation collusion probe the "little push" it needs to come to a conclusion.
He graduated magna cum laude from New York University Law School in 1968 and was appointed US attorney for the Southern District of New York in 1983.
White House lawyer Ty Cobb confirmed the move to CNBC.
The entry of Giuliani, an experienced attorney with a combative reputation, immediately raises questions about how Trump will engage with Mueller and the leadership at Justice. "So the symbolism of Rudy being hired on President Trump's team [is huge]". But what exactly is Giuliani's role going to be?
Mr. Giuliani has truly forgotten where he came from. Experts claimed Trump seemed like a tough client who does not pay heed to his lawyers' advice and some may fear potential conflict of interests, thus avoiding the job altogether.
A number of Trump allies have believed that Trump has been ill-served by his current legal team and applauded the addition of the hard-charging Giuliani.
Giuliani will be taking a leave of absence from his law firm, Greenberg Traurig, according to a statement from the firm.