“I’ve always promised that I would do the work, even when it was hard, uncomfortable, or unpopular," he said in a statement.
"That work continues, which is why after careful consideration and prayer, and with the support of my family, I’m asking South Dakotans for the opportunity to continue serving them in the U.S. Senate," Thune added.
His decision came later than expected — he pushed the announcement until after the holidays as he grappled with his next steps — and brings relief to congressional allies who have been urging him to stay in the Senate, including Minority Leader Mitch McConnell, R-Ky.
Thune, 61, who is currently serving his third term, was first elected in 2004 when he defeated then-Senate Majority Leader Tom Daschle, D-S.D. He then went on to easily win both his reelection bids in a deeply red state, which has benefited from an outsized influence in D.C.
As Senate Minority Whip, the top GOP vote counter, Thune is considered a leading potential successor to McConnell once he retires.
McConnell urged Thune to seek reelection last month when asked to comment about the possibility of his retirement. "I certainly hope he won't," McConnell said in an interview with conservative radio host Hugh Hewitt. "Thune is an outstanding senator. He's done a great job as whip ... It would be a real setback for the country and our party if he retires."
Speaking to reporters on the Capitol, Thune recently said the biggest motivator for his contemplating retirement was his family, while also noting that the current political environment in the Republican Party would also factor into his decision.
“I think in the broader general ether of the political environment that we're in, you know, those are all factors you take into consideration, but a lot of it ends up being a lot more personal stuff,” he said.
A member of the old guard of conservative politics, Thune has shown signs of weariness after navigating a Congress and GOP marked by Trump, who fired back at Thune last year when the senator criticized his attempt to challenge the results of the 2020 election. The former president carried South Dakota by a margin of 26 percent over President Joe Biden in the 2020 election.
After Thune said any challenge to Biden's win "would go down like a shot dog," Trump called him a "RINO" — Republican In Name Only — and threatened to launch a primary challenge against him.