Sen. Patrick Leahy, D-Vt., will not seek re-election at the end of his term, he told reporters in his home state Monday.
"It is time to pass the torch to the next Vermonter who will carry on this work for our great state. It’s time to come home," Leahy said in an announcement at the State House in Montpelier.
Leahy, 81, is the longest-serving current senator, having served since 1975. He is chair of the Appropriations Committee and third in the line of succession to the presidency as president pro tempore of the Senate, after the vice president and the speaker of the House. He was last re-elected in 2016.
Leahy was hospitalized and under medical observation this year after he felt unwell.
The Senate is divided 50-50 between Republicans and Democrats, with Democratic Vice President Kamala Harris as the tiebreaking vote. If a seat were to become vacant or a senator were unable to attend votes, the balance of power could be upended.
Notably, Leahy presided over former President Donald Trump's second impeachment trial.
"When I preside over the impeachment trial of former President Donald Trump, I will not waver from my constitutional and sworn obligations to administer the trial with fairness, in accordance with the Constitution and the laws," he said in a statement at the time.
The seat should be safe for Democrats, although Republicans are expected to hold the electoral advantage going into the 2022 midterm elections. President Joe Biden won Vermont by 35 percentage points last year.
The state's other senator, Bernie Sanders, an independent who caucuses with the Democrats, is considered one of the most liberal members of the Senate.
Democratic Rep. Peter Welch, who represents the entire state in its single congressional district, is seen as the most likely person to replace Leahy. He he has not announced his intention to run.
In a statement, Welch said that Leahy's retirement was "historic and bittersweet" and that "it is hard to imagine the United States Senate without Patrick Leahy."
Leahy was the first, and he remains the only, Democrat elected to the Senate from Vermont, despite its famously progressive culture. Liberal Yankee Republicans used to rule the state, a legacy carried on by Gov. Phil Scott, a popular moderate Republican who is also one of the state's winningest race car drivers.
Scott has said in the past that he has no interest in running for the Senate, but some in the GOP hope to change his mind, believing he is the only Republican who could mount a real run.
Senate Majority Leader Chuck Schumer, D-N.Y., signaled confidence that Democrats can hold on to the seat.
"Very few in the history of the United States Senate can match the record of Patrick Leahy. He has been a guardian of Vermont and more rural states in the Senate, and has an unmatched fidelity to the Constitution and rule of law," Schumer said in a statement. “With Patrick’s help, we are confident Democrats will retain the seat."
Leahy is known on Capitol Hill for his cameos in Batman films — he has appeared in five since 1995's "Batman Forever" — playing himself or a fictional political leader terrorized by Gotham City's villains.
He will not, however, reprise the role in the coming film "The Batman," telling the Burlington Free Press last year, "I have too many other things going on with Covid, with appropriation bills."
Leahy, an amateur photographer, is also known for documenting meetings with world leaders and historic events on Capitol Hill through the rare perspective of a true insider.
One of Leahy's former teachers — a 92-year-old nun who taught chemistry at the Catholic school he and his sister attended — was among those who showed up at the State House for his announcement.
David Carle, a spokesman for the senator, said she told Leahy that she was proud of him.
"She heard on the radio this morning that the senator would be in the State House, and she decided to come to wish him well," Carle said.