An aide to six-term Sen. Thad Cochran of Mississippi says the lawmaker will run for re-election.
The Republican has been in the Senate since 1978, after serving six years in the House. He turns 76 on Saturday.
Cochran is the top GOP lawmaker on the Agriculture Committee and a senior member of the Appropriations panel. His decision puts to rest speculation that he wouldn't seek another term. A tea party-backed candidate, Chris McDaniel, has announced he would seek the seat, setting up a primary fight.