John O’Toole, who ran for City Council in 2011, said on Thursday he plans to be a candidate in the upcoming special election to replace Marty Walsh in the House.

Walsh resigned from his House seat on Jan. 3, days before becoming the forty-eighth mayor of the city of Boston. Walsh served in the seat for 16 years after winning a special election in 1997.

“These opportunities don’t come around a lot,” O’Toole said.

O’Toole, a longtime Cedar Grove neighborhood activist, made a bid for the District 3 Council seat when Maureen Feeney decided against running for another term. She was first elected in 1993 and is now the city clerk.

Frank Baker of Savin Hill won the race, picking up 5,252 votes to O’Toole’s 4,120 votes. The battle had a City-Hall-versus-the-State-House dynamic, with Walsh backing Baker and Feeney, along with then-Mayor Thomas Menino, backing O’Toole.

On Thursday, O’Toole posted a note to supporters on Facebook. “My 25 years as a neighborhood activist, and 25 years as a proud member of Plumber’s Union Local 12 afford me the qualifications to serve the 13th District well,” he wrote. “I look forward to earning your support, and anticipate a great campaign.”

A number of contenders are already in: former State House aide Dan Hunt, local activist Gene Gorman, and attorneys Liam Curran and PJ McCann have pulled nomination papers. Tony Dang, a MBTA police officer who is active in Dorchester’s Vietnamese community, is a potential candidate.

The Dorchester-based district, which includes a precinct in North Quincy, is a Democratic one, meaning the March 4 primary will be determinative. The general election is on April 1, and the winner will have to run again in the fall to keep the seat.

Candidates must turn in 150 signatures to local elections officials by Tuesday, Jan. 21.