House Democrats formally elevated Representative Hakeem Jeffries of New York to be their leader on Tuesday, uniting around a liberal lawyer and disciplined political tactician as the face of their opposition to the new Republican majority.

On a day otherwise consumed by raucous infighting among Republicans, Mr. Jeffries’s ascent made history. He is the first Black politician to lead either party in Congress. And, at 52, he represents a generational change for House Democrats after two decades under Representative Nancy Pelosi.

Mr. Jeffries was expected to emerge from Tuesday’s balloting as the House minority leader, given the Republicans’ narrow majority. With the Republican Party fracturing, he ended up receiving more support in the first two rounds of voting for speaker than the main Republican candidate, Representative Kevin McCarthy of California — but not the majority needed to win.

Democrats wasted little time using the votes to try to embarrass Republicans, weaponizing the differences between Mr. Jeffries and Mr. McCarthy, a close ally of former President Donald J. Trump. (Republicans are certain to make their own attempts to vilify Mr. Jeffries in the months ahead.)

“He does not traffic in extremism. He does not grovel to or make excuses for a twice-impeached, so-called former president,” Representative Pete Aguilar of California, the No. 3 Democrat, said of Mr. Jeffries in a nominating speech on the House floor. “He does not bend a knee to anyone who would seek to undermine our democracy because, Madam Clerk, that’s not what leaders do.”

A son of civil servants who cut his teeth as a litigator at a white-shoe law firm and at CBS, Mr. Jeffries rose swiftly through the ranks of Democratic politics in New York and then Washington. Since 2013, he has represented some of the nation’s most iconic Black neighborhoods in Brooklyn. During the Trump presidency, he built a national profile as a sharp-tongued critic and impeachment prosecutor, while also working with Republicans to pass criminal justice reform legislation.

Democrats have been preparing Mr. Jeffries, the former chairman of the House Democratic Caucus, for several years as a potential leader. But it was only after Ms. Pelosi decided to resign as speaker after last year’s midterm elections that he stepped forward, alongside Mr. Aguilar and Representative Katherine Clark of Massachusetts, his top deputies.

Allies say Mr. Jeffries is an exceptionally calm strategist and communicator, and in Washington, he has become known for sticking to carefully worded statements. But he faces no easy task: taming an unruly and ideologically diverse Democratic caucus as he tries to blunt Republican attacks on the Biden administration and win back the majority in 2024.