Shenna Bellows, who’s seeking the Democratic Party nomination, tweeted a photo of herself outside the Muskie Building in Augusta, declaring that she’d filed paperwork necessary to become a candidate.

Bellows, 38, resigned a little more than a week ago after more than eight years with the American Civil Liberties Union of Maine.

Bellows is planning campaign kickoff events in Ellsworth and Portland on Oct. 23. She said Tuesday that she decided to run while working with Republicans and Democrats last session to come to an agreement on legislation that strengthens Maine’s laws on cellphone privacy.

“We need more courage and honesty and willingness to sit down with people who have different viewpoints and have honest conversations and move forward positive change,” said Bellows, an attorney from Manchester.

Bellows is the first to announce a challenge to Collins, a moderate Republican senator born in Caribou. She took office in 1997 and has said she intends to run for re-election to preserve the seat, which is seen as important for Republicans’ push to win the Senate majority.

Bellows has never run for public office, but this will not be her first campaign. She helped lead the ballot-measure campaign to approve same-sex marriage in Maine last year.

“I recognize the power of the incumbency, but I am excited to talk about issues of economic fairness and constitutional freedoms,” she said.

Papers filed for US Senate at the Post Office, Muskie Building in Augusta. Official launch October 23! #mepolitics pic.twitter.com/yVtOetOzVA

— Shenna Bellows (@shennabellows) October 8, 2013