WASHINGTON — The Senate confirmed President Biden’s 40th federal judicial nominee early on Saturday morning, the most judges confirmed in a president’s first year in the last 40 years.

In a pre-dawn mad dash before leaving Washington for the holidays, lawmakers confirmed 10 district court judges, bringing the year-end total to 40 and notching an achievement not seen since former President Ronald Reagan. It underscored how the White House has set a rapid pace in filling vacancies on the federal bench, even besting the records set by the Trump administration, which maintained a laser focus on reshaping the judiciary.

The milestone came as a welcome victory for frustrated congressional Democrats whose legislative agenda continues to hit roadblock after roadblock, including their attempts to pass Mr. Biden’s signature social safety net, climate and tax bill, and their efforts to bolster voting rights and overhaul immigration.

The Senate confirmed 18 circuit and district court judges in President Donald J. Trump’s first year in office, and 12 in President Barack Obama’s inaugural year.

Mr. Biden, a former chairman of the Senate Judiciary Committee, pledged to counter the Trump era’s aggressive efforts to transform the judiciary with young right-wing judges who are mostly white and male. Since January, the president has sent the Senate an extraordinarily diverse roster of nominees, both in terms of ethnic background and professional experience.

Many of the nominees confirmed were “firsts” — including the first Muslim American federal judge and the first openly lesbian judge to serve on any federal circuit court. And Mr. Biden’s administration has also taken pains to nominate not just corporate attorneys, but public defenders and civil right attorneys.

“Because of the commitment to restoring the federal judiciary by President Biden and Senate Democrats,” said Senator Chuck Schumer of New York, the majority leader, “it is no longer a bench that is simply prosecutors, partners in large law firms — but rather many, many others from walks of life with different and needed perspectives on the federal bench, such as public defenders, civil rights lawyers, election experts and more.”

Mr. Biden and Mr. Schumer “not only shepherded more confirmations in Biden’s first year than any president in recent history; they have led a revolution in the way Democrats think about who should serve as judges by selecting lawyers who have represented everyday people,” said Christopher Kang, the chief counsel of Demand Justice, a progressive advocacy group that was created after the 2016 presidential election and the Republican stonewalling of Mr. Obama’s final Supreme Court nominee.

The rapid speed of confirmations this year came despite an evenly divided Senate, with Vice President Kamala Harris serving as a tiebreaker. But like Mr. Biden’s legislative agenda, his judicial agenda is also facing challenges of its own.

Democrats have overwhelmingly racked up judicial victories in states represented by two Democratic senators. They are facing stronger headwinds in states represented by at least one Republican senator. Tennessee Republicans have already raised objections to Mr. Biden’s pick for an influential appeals court there, the administration’s first judicial nominee from a state represented by two Republican senators.

Beyond Republican-led efforts to slow-walk such nominees, Mr. Biden is also facing limited appellate vacancies from Republican appointees — which means he has little room to reshape the ideological balance of the courts. Of the appellate nominees Mr. Biden has named, only three of 10 would replace Republican appointees.

At the moment, the vacancies Mr. Biden is facing in the appeals courts are those created by Democratic appointees, said Russell Wheeler, a visiting fellow at the Brookings Institution who studies the federal courts. “So far, the percentage of Republican appointees on the court of appeals is almost unchanged from when Biden took office,” he said.

The greatest threat the administration’s effort may face, however, is the risk of losing control of the Senate in the 2022 midterm elections. Mr. Wheeler noted that Mr. Trump had nominated 54 circuit court judges over four years with a Republican-controlled Senate.

“If Biden loses the Senate, it’s not going to be talking about ‘How many appointees,’” Mr. Wheeler said. “It’s going to be talking about whether there’s going to be any at all.”

In total, Mr. Biden has sent 71 judicial nominees to the Senate for consideration.

The Senate also early Saturday confirmed on a voice vote 41 ambassadors, including Rahm Emanuel, the former mayor of Chicago, as U.S. ambassador to Japan. That vote came about as part of a deal with Senator Ted Cruz, Republican of Texas, who had blocked the nominees in his push for a vote on sanctions over a Russian-backed gas pipeline. After Mr. Cruz finally won a promise for a vote on the sanctions, Mr. Schumer was able to push the nominees through.