At least three ethics complaints had been publicly filed against Mr. Giuliani, including one earlier this year by a group of prominent lawyers who accused him of abusing the court system to undermine democracy. It is not known which complaint, if any, triggered the New York court’s investigation.
Mr. Giuliani is also licensed to practice law in Washington, D.C., and the decision in New York could set off disciplinary proceedings there, although that is not automatic.
It is rare for the court to temporarily suspend lawyers for making unethical public statements, according to lawyers who specialize in disciplinary proceedings, and it is more common in cases in which lawyers are accused of stealing money from clients.
The practical impact of the decision was not clear. Although Mr. Giuliani started his own law firm in 2019, it has been decades since he regularly argued in courtrooms. Before Mr. Giuliani became Mr. Trump’s lawyer, he was running his own security consulting business. More recently, he has hosted a radio show and appeared in cigar commercials.
Still, the suspension marked another stunning chapter in the rise and fall of Mr. Giuliani, once a legal and political star. He had enjoyed near-hero status when, as New York City mayor, he led the city through the Sept. 11, 2001, terrorist attacks.
Before that, he was a hard-charging prosecutor who was known for battling organized crime and corrupt politicians. But he is now being investigated by the United States attorney’s office in Manhattan, the same office he once led, and faces the prospect of being banned from the legal profession in which he has worked for more than five decades.
The federal investigation into Mr. Giuliani centers on his dealings in Ukraine before the 2020 election, when he sought to damage President Biden’s credibility. In April, F.B.I. agents seized Mr. Giuliani’s cellphones and computers, an extraordinary action to take against a lawyer for a former president.