Curtis's selection on Saturday follows Sen. John Walsh (D-MT) dropping out of the Senate race following a plagiarism scandal centered around Walsh's master's thesis.
Democrats, as a result, had to hold a special convention to pick a new nominee to race Daines.
Curtis is a high school math teacher with strong support from Montana unions, according to The Los Angeles Times.
Curtis beat rancher Dirk Adams in the nominating convention to get the Democratic nomination. She's expected to face an uphill battle to beat Daines with just a few months before the general election.
In an interview with The Daily Beast Curtis said if she won the Senate seat her first priority would be campaign finance reform. But, the Daily Beast notes, Curtis still has to figure out a number of positions, including on recent events in Iraq.
"I'm still studying a lot of these issues," Curtis said. "I'm planning to listen to all sides and make these decisions listening to regular Montanans."