The Utah Republican, who has been a vocal Trump critic, leaves office in 2025.
Utah Republican Sen. Mitt Romney will not seek reelection in 2024, he announced Wednesday -- marking the potential end to a storied conservative career that had in recent years put him in conflict with his party's standard-bearer, Donald Trump.
In a video statement, Romney, 76, touted his role in major pieces of bipartisan legislation on issues including infrastructure, guns and COVID-19 relief but said it was time for a "new generation" to take the reins -- both on Capitol Hill and in the White House, accusing President Joe Biden, 80, and former President Trump, 77, of not doing enough to address America's challenges.
Romney, a former Massachusetts governor and the 2012 GOP presidential nominee, was elected to the Senate in 2018 and will leave Washington in January 2025.
At a news conference on Wednesday afternoon, Romney invoked his own age as part of the move to retire.
"It's time for guys like me to get out of the way," he told reporters.
"Over the last couple decades, people of my age -- the boomers -- have done pretty well for ourselves," he said, "and we voted for all sorts of benefits and programs for us and we've paid for them and think some of the people coming along next want to have a say in how we leave the earth and how they prepare for the future."
In his recorded statement, he said, "I have spent my last 25 years in public service of one kind or another. At the end of another term, I'd be in my mid-eighties. Frankly, it's time for a new generation of leaders. They're the ones that need to make the decisions that will shape the world they will be living in."
"We face critical challenges -- mounting national debt, climate change and the ambitious authoritarians of Russia and China. Neither President Biden nor former President Trump are leading their party to confront them," Romney added. "Political motivations too often impede the solutions that these challenges demand."
Still, Romney insisted he wouldn't entirely leave politics, noting that his Senate term lasts for over another year and hinting he'd remain involved beyond his departure.
"While I'm not running for reelection, I'm not retiring from the fight. I'll be your United States senator until January 2025. I will keep working on these and other issues and I will advance our state's numerous priorities. I look forward to working with you and with folks across our state and nation in that endeavor," he said, speaking to Utahans.
Romney's announcement caps months of speculation over whether he would seek a second term in the Senate.
He was one of the GOP's few high-level officeholders to consistently criticize Trump, ultimately voting to convict Trump in each of his impeachment trials -- attacks that fueled both discussion over Romney's place in a party reshaped in Trump's image and questions over whether he would even be able to win a primary in another campaign.
Romney told ABC News following his announcement that "there's no question that the Republican Party today is in the shadow of Donald Trump."
"Look, my wing of the party talks about policy, and about issues that will make a difference to the lives of the American people. The Trump wing of the party talks about resentments of various kinds and getting even and settling scores and and revisiting the 2020 election," he said.
He dismissed the idea that his decision not to seek a second term had something to do with the possibility of Trump appearing on the 2024 ballot.
"The people in Utah don't all agree with me at the posture I took with regards to Donald Trump, but they respect people who vote their conscience and I appreciate that and my fellow citizens and I don't have any question on mine that I don't want to fight or run again. I just don't think that we need another person and their age. I'm a little longer tooth already," he said.
Romney also told ABC News that Biden called him following the announcement.
Riverton Mayor Trent Staggs is the only Republican officially in the 2024 Utah Senate GOP primary race so far, but state House Speaker Brad Wilson has launched an exploratory committee and former Rep. Jason Chaffetz is weighing a campaign, too.
"We are at a crossroads, and it's never been more important to elect a strong conservative fighter to the U.S. Senate. The stakes are too high, and we need a leader with the guts to stand up and get things done for the people of this state. I've been encouraged so far by the record-breaking fundraising, groundswell of grassroots support, and unprecedented endorsements we've received so far," Wilson said in a statement.
Chaffetz said in a text message to ABC News that Romney's retirement would not change his decision-making.
Romney's camp, meanwhile, has swatted away worries over his vulnerability in a primary, citing local polling suggesting he would have been able to run a muscular campaign.
"He made his decision from a position of strength and on his own terms," Romney spokesperson Liz Johnson said on Wednesday.
Romney did enjoy support from the GOP's establishment flank, with Senate GOP Leader Mitch McConnell praising him after news of his retirement broke.
"The U.S. Senate is known to attract bright and proven public servants. However, we rarely get to welcome new Senators already as accomplished and well-regarded as Mitt Romney. The Senate has been fortunate to call our friend from Utah a colleague these past four and a half years, and I am sorry to learn that he will depart our ranks at the end of next year," McConnell said in a statement.
In an interview with The Washington Post, Romney admitted his Trump criticism had left him somewhat adrift in the Republican Party and that while he would like to see another candidate win the party's 2024 presidential nomination besides Trump, he suggested his endorsement wouldn't serve to help any candidate.
"I'm not looking to get involved in that," he said.
While it's unclear what his post-Senate political involvement will look like, Romney insisted to the Post that he won't run for president on the potential No Labels third-party ticket, warning it could spoil Biden's campaign for reelection.
"I lobby continuously that it would only elect Trump," he said.
ABC News' Rachel Scott contributed to this report.