AUGUSTA — Betsy Sweet, a longtime progressive activist and lobbyist, filed paperwork Monday to run for governor on the Democratic ticket.

Sweet, of Hallowell, joins two other Democrats who have already filed in what is expected to be a crowded field for the party’s nomination. Sweet is a well-known lobbyist and advocate on women’s issues, the environment, people with disabilities and other progressive issues. A former director of the Maine Women’s Lobby and the Maine Commission for Women, Sweet now runs the Moose Ridge Associates lobbying firm.

In announcing her candidacy Monday, Sweet highlighted her decades of experience working at the State House.

“If we want to change things for the better, we must get big money out of politics,” Sweet said in a statement. “From there, we create a government on Maine values: build on people’s strengths, enlist the support of family, friends and neighbors, keep our aim high, and work hard together. These are the values Mainers share. It’s the life I’ve lived. I want to bring these values back to Maine government.”

Sweet plans to use Maine’s public campaign financing system, also known as Maine Clean Elections, for her campaign.

Two other people have already filed their candidacy paperwork to seek the Democratic nomination for governor: veteran and attorney Adam Cote of Sanford and retired Coast Guard commander and health care executive Patrick Eisenhart of Augusta. Additional candidates are expected to join the primary race.

On the Republican side, Sen. Susan Collins has said she is considering running, and Mary Mayhew, who resigned last week as commissioner of the Maine Department of Health and Human Services, is regarded as a prospective candidate.

Other candidates who have filed include: State Treasurer Terry Hayes, who is running as an independent; Libertarian Richard Light and Republican Deril Stubenrod.