Giuliani's work on matters related to Ukraine and his business dealings with two Soviet-born associates has been the subject of an ongoing investigation by prosecutors in the Southern District of NY, sources previously told ABC News.
Giuliani, the former New York City mayor once celebrated for his leadership in the aftermath of the 9/11 attacks, has been under federal scrutiny for several years over his ties to Ukraine.
Investigators executed warrants at Giuliani's home on Madison Avenue and his office on Park Avenue and seized electronic devices, a person familiar with the investigation told the AP.
The officials could not discuss the investigation publicly and spoke to the AP on condition of anonymity.
He later won wide acclaim and national fame as "America's Mayor" for his efforts in helping New York City deal with and recover from the September 11, 2001 attacks.
A doorman is seen at Giuliani's Manhattan apartment building Wednesday.
While the search warrant does not mean Giuliani committed a crime, it signals that investigators persuaded a judge they believed criminal conduct occurred and that executing the warrant might uncover relevant evidence.
Giuliani has been the focus of an investigation concerning his activities in Ukraine.
U.S. investigators search Rudy Giuliani's Manhattan home, office
Mr. Costello said the warrant sought communications between Mr. Giuliani and individuals including John Solomon, a columnist who was in communication with Mr. Giuliani about his effort to push for investigations of Joe Biden in Ukraine.
Michael Cohen, a former personal lawyer to Trump who has become a critic of his former boss, tweeted: "Here we go folks!"
Giuliani's lawyer, Robert J. Costello, responded to the raid, stating, "What they did today was legal thuggery". Giuliani himself had previously called the investigation "pure political persecution". Those efforts led to Trump's second impeachment trial after he left office.
Members of the media gathered outside Giuliani's apartment Wednesday.
The full scope of the investigation is unclear, but it at least partly involves Rudy Giuliani's dealings in Ukraine, law enforcement officials have confirmed.
The Justice Department was widely expected to revisit the issue once Attorney-General Merrick Garland assumed office.
Mr Garland was confirmed last month and Deputy Attorney-General Lisa Monaco was confirmed to her position and sworn in last week.
The Justice Department requires applications for search warrants served on lawyers be approved by senior department officials.
CDC may soon update outdoor face mask wearing guidance
On Oct. 7, Fauci reiterated that being outside is "much less of a risk, but it is a risk". President Joe Biden will address the nation Tuesday, three inside sources told CNN .