Giuliani joined Trump's legal team in April with the goal of helping to deal with the Russia investigation, according to CNN. Special counsel Robert Mueller is investigating Russian meddling in the 2016 presidential election and its possible ties to Trump and his campaign officials, among other things.
Giuliani had taken a leave of absence from law firm Greenberg Traurig.
"In light of the pressing demands of the Mueller investigation, I believe it is in everyone's best interest that I make it a permanent resignation," Giuliani said Thursday in a statement obtained by CNN. "This way, my sole concentration can be on this critically important matter for our country."
Here are some things to know about Giuliani:
- Giuliani was born May 28, 1944, to a working-class family in Brooklyn, New York. His grandparents were Italian immigrants and from them Giuliani said he learned the importance of having a strong work ethic.
- He previously joined the U.S. Attorney's Office in 1970, where he served in various roles. President Ronald Reagan in 1981 appointed Giuliani to serve as associate attorney general, the third highest position in the Justice Department. From 1983 to 1989 he served as U.S. Attorney for the Southern District of New York.
- In 1989, Giuliani entered the race for mayor of New York City as a candidate of the Republican and Liberal parties, losing by the closest margin in City history. However in 1993, his campaign focusing on quality of life, crime, business and education made him the 107th Mayor of the City of New York. In 1997 he was re-elected by a wide margin, carrying four out of New York City's five boroughs.
- Giuliani unsuccessfully ran for New York City mayor in 1989 as a candidate of the Republican and Liberal parties.
- He ran again in 1993 and won, becoming New York City's 107th mayor. He was re-elected in 1997 and lead the city in the immediate aftermath of the Sept. 11, 2001 terror attacks.
- The Queen of England made Giuliani an honorary knighthood in the wake of the Sept. 11, 2001 attacks. Queen Elizabeth gave Giuliani the insignia of a Knight Commander of the Order of the British Empire in 2002, The Telegraph reported.
- Giuliani in 2008 ran for the Republican party's presidential nomination, but he withdrew amid lackluster primary numbers and threw his support behind the party's eventual nominee, John McCain.
- Giuliani was a staunch and steady supporter of Trump before voters went to the polls for the 2016 presidential election.