The Montana Democratic Party on Saturday selected Amanda Curtis to replace U.S. Sen. John Walsh, D-Mont., as the party's nominee for the seat, which is up for re-election in November.
Walsh said last week he would not seek a full term amid allegations he plagiarized his master's thesis at the Army War College.
Montana Gov. Steve Bullock appointed Walsh to the senate seat in February to replace Sen. Max Baucus, who was appointed by President Obama to be ambassador to China.
Curtis, 34, is a member of the Montana House of Representatives and teaches math. She'll face Republican nominee Steve Daines in November.
"This election could decide who controls the Senate, and I don't mean the difference between Republicans and Democrats," Curtis said. "I mean the difference between the millionaires and the middle class."