Instead, Noem said, she'll run for reelection to the House. Noem pledged to work to help a Republican win back the seat to be vacated by retiring Sen. Tim Johnson (D-S.D.).
In late May, Noem told The Hill that she was discussing a potential Senate run with groups interested in her candidacy, though she wouldn't elaborate.
She was considered a more conservative alternative to the only announced Republican in the race, former Gov. Mike Rounds.
But some Republicans were worried that if Noem launched a primary challenge against Rounds, that would ultimately weaken the eventual nominee and jeopardize Republican chances at the seat.
Noem's decision not to run eliminates a hurdle to Rounds's nomination, but outside conservative groups are still actively looking for a potential challenger.