Sen. Lamar Alexander will not run for re-election in 2020, he announced Monday.
The 78-year-old Tennessee Republican will serve out the rest of his current term. In a statement, Alexander said, "it is time for someone else to have that privilege" of representing the state in the Senate.
"I have gotten up every day thinking that I could help make our state and country a little better, and gone to bed most nights thinking that I have," he said. "I will continue to serve with that same spirit during the remaining two years of my term."
Alexander has represented Tennessee in the Senate since 2003. He also had stints as the U.S. Education secretary and as his state's governor. Alexander serves as chairman of the Senate Health, Education, Labor and Pensions Committee, a term limited position.
His retirement will follow the departure of fellow Tennessee GOP Sen. Bob Corker, who will leave office next month. Republican Rep. Marsha Blackburn beat Democratic former Gov. Phil Bredesen by more than 10 percentage points in the November race to succeed Corker.
In a statement Monday, Corker called Alexander "one of the finest statesmen our state has ever seen" who will "leave behind a remarkable legacy."
November's result suggests the Republican candidate in the 2020 race for Alexander's seat will likely enter as a favorite. Before the senator announced he would not run, nonpartisan forecaster Cook Political Report rated the seat as "solid" Republican.
Bredesen, a former statewide election winner who ran as a moderate, was seen as a strong candidate with a fighting chance to snatch an open Senate seat despite Tennessee's pro-Trump leaning. But Blackburn was one of several GOP Senate candidates who outperformed polls leading up to November's elections.
Republicans kept control of the Senate and will hold a 53-47 majority next month. Democrats won control of the House by gaining 40 net seats.
Alexander led the Senate health committee during the ultimately unsuccessful GOP efforts to repeal and replace the Affordable Care Act last year. The Republicans' health-care overhaul was unpopular, and played a role in the GOP losing control of the House.
He recently helped to shepherd bipartisan bills through Congress to promote medical innovation and fight the opioid crisis. He unsuccessfully sought the Republican nomination for president in 1996 and 2000.