Bellows tweeted Tuesday that she had filed her papers to challenge Collins in 2014, and that her official kickoff will come on Oct. 23.
According to the Kennebeck Journal, Bellows has worked closely with Democrats and Republicans in the statehouse and has developed a reputation as a "powerbroker." She's focused particularly on marriage equality and voter rights issues throughout her career.
Collins is well-liked and expected to win reelection in 2014, despite the blue lean of the state.
In a statement, Maine Democratic Party Chairman Ben Grant indicated Democrats will attempt to nationalize the race and hook Washington GOP baggage around Collins' neck.
“Shenna has spent her career working tirelessly for Mainers, and we know she’ll do the same during this campaign,” he said. “Collins has demonstrated that she is powerless to stop the extreme rightward lurch of the GOP. It’s time for a change to someone with clear, consistent values that match the values of people across Maine.”