President Trump said on Saturday that he would nominate James M. McDonald to be the next U.S. attorney in the Southern District of New York, again choosing one of his personal lawyers for one of the nation’s most powerful legal positions.

Mr. Trump praised Mr. McDonald, pointing to his extensive credentials. He is “a former Assistant U.S. Attorney in the Southern District of New York, and served as Director of Enforcement at the U.S. Commodity Futures Trading Commission during my First Term,” Mr. Trump wrote. Mr. McDonald was also a law clerk to Chief Justice John G. Roberts Jr.

Mr. McDonald would replace Jay Clayton, Mr. Trump’s choice to be the next director of national intelligence after his temporary pick for that role, Bill Pulte — a top federal housing official — set off widespread concerns among Republican senators for his lack of intelligence experience and his zeal in pursuing Mr. Trump’s perceived enemies. Mr. Clayton still requires Senate confirmation.

Mr. McDonald, who goes by Jamie, is a litigation partner at Sullivan & Cromwell, the law firm handling Mr. Trump’s appeal of his criminal conviction in a Manhattan state court on 34 felony counts of falsifying business records in connection with concealing a hush-money payment to a porn star during the 2016 presidential campaign.

Mr. McDonald is a member of the Trump appeals team for that case.

It was the Southern District of New York, historically one of the most independent federal prosector offices in the country, that paved the way for several of Mr. Trump’s personal legal problems over the last eight years, beginning in his first term.

The special counsel investigating a possible conspiracy between Russia and the Trump 2016 campaign referred a spinoff investigation of Mr. Trump’s then-personal lawyer and fixer, Michael D. Cohen, to the Southern District. Part of that investigation related to Mr. Cohen’s payment to a porn star, Stormy Daniels, to stop her from going public with a claim of a past affair with Mr. Trump while he was the Republican nominee in 2016.

Mr. Cohen pleaded guilty to campaign finance violations for those payments, which he said was at the direction of Mr. Trump. That paved the way for Mr. Trump’s own criminal conviction in 2024, in a prosecution brought by the Manhattan district attorney, Alvin Bragg.

The Southern District also indicted Jeffrey Epstein, the sex trafficker who counted Mr. Trump, Bill Clinton, Bill Gates, the former Obama White House counsel Kathy Ruemmler, and others among his contacts. Mr. Epstein died in prison before his trial. His longtime co-conspirator, Ghislaine Maxwell, was convicted of sex trafficking in the Southern District in 2021 and sentenced to 20 years in prison.

In the U.S. attorney’s office, which is based in Manhattan, Mr. McDonald was a well-regarded assistant U.S. attorney and a member of the team that prosecuted Sheldon Silver, the once powerful Democratic speaker of the New York State Assembly who was convicted in 2015 on corruption charges. (The conviction was overturned on appeal, and Mr. Silver was retried and again convicted, and sentenced to seven years in prison. He died in 2022.)

Unlike Mr. Clayton, who served in Mr. Trump’s first term as the chairman of the Securities and Exchange Commission and made appearances on CNBC before and during his tenure as U.S. attorney, Mr. McDonald has kept a much lower profile.

“He has a rare combination of super high IQ and EQ,” Steven R. Peikin, a friend, partner at Sullivan & Cromwell and fellow Southern District alumnus, said on Saturday. He said Mr. McDonald would be “a terrific leader” of the Southern District, where he would oversee about 200 assistant U.S. attorneys handling criminal and civil cases.

The acting attorney general, Todd Blanche, another former Trump personal lawyer who also once worked in the Southern District, described Mr. McDonald as “my friend” in a congratulatory post on X.

During his time at Sullivan & Cromwell, Mr. McDonald represented two corporate clients — Live Nation, the music concert promoter, and Polymarket, the prediction market — that received favorable treatment from the Justice Department under Mr. Trump.

In March, the department’s antitrust division settled claims against Live Nation, one week into a high-profile trial that examined competition in the music industry.

And last July, federal prosecutors in Manhattan closed a criminal investigation into Polymarket that arose from allegations of wrongdoing stemming from online wagers on elections.

Before clerking for Justice Roberts, Mr. McDonald spent a year working in the White House Counsel’s Office under President George W. Bush. He is a graduate of Harvard and the University of Virginia Law School.

Nicholas Biase, a Southern District spokesman, said in a statement that Mr. McDonald is “widely respected,” and that “the office welcomes the president’s choice to lead the S.D.N.Y.”

William K. Rashbaum and Ben Protess contributed reporting.