Portland voters will get an opportunity in March to expand ranked-choice voting to all city elections.

The City Council voted unanimously Monday night to place a charter amendment to expand ranked-choice voting to City Council and school board races on the March 3 ballot, when voters are expected to head to the polls en masse for the presidential primary.

Portland already chooses its mayor using ballots that allow voters to rank their preferences. It is the only municipal race in Maine to use ranked-choice voting.

The effort to expand ranked-choice voting to all local elections was initially led by Fair Elections Portland, but the group failed to gather enough signatures to place it on the ballot.

Campaign Chairwoman Anna Kellar thanked the council for picking up the effort.

“We fell short of the required signatures, but felt there was strong support in the city, so we’re thanking you for bringing that forward tonight and getting this out to voters,” Kellar said.

Ranked-choice voting has been used in the city’s mayoral election since 2011. The voting method was extended by the Legislature to statewide primaries and federal races last year.

In a ranked-choice election, voters rank the candidates in order of preference. If no candidate gets more than 50 percent of the first-choice votes, the last-place candidate is eliminated and their ballots are redistributed to the other candidates based on the second or third choices. That instant-runoff process continues until one candidate gets more than 50 percent of the votes.

On Nov. 5, the city’s four-way mayoral race was decided by ranked-choice voting and an instant runoff, but the five-way race for the District 3 seat was not. The original order of the mayoral race did not change. Kathleen Snyder won the first round with 39 percent of the vote and ended with 62 percent after two runoffs. On the other hand, Tae Chong won the five-way District 3 council race with 43 percent of the vote.

“Ranked-choice voting will ensure, in multicandidate contests for City Council and school board, that city officials are not elected by narrow pluralities but will instead be elected by the reference of a majority of voters,” resident Scott Vonnegut said.

City Clerk Katherine Jones had recommended putting a charter amendment for ranked-choice voting on the ballots for the election in June, because of the $12,000 cost for a March election. She also cited historically low turnout at March presidential primaries in 1996 and 2000 as another reason.

A strong turnout is needed because at least 30 percent of voters who cast ballots in the previous gubernatorial election need to cast ballots on a charter amendment for the results to be valid. That means a minimum of either 9,982 or 10,226 ballots will need to be cast, depending on whether the city applies that percentage to the number of ballots cast in the governor’s race (33,276) or the number of ballots cast during that election (34,087) – a previous point of contention between the city and Fair Elections Portland.

Kellar said the previous primaries were not really contested and were not a good comparison.

“This is going to be a high turnout election in March, we have no guarantee of that in June,” Kellar said. “It would be such a shame to send this out to voters and have this not be able to go in effect because we didn’t have enough people voting.”

While Fair Elections Portland supported the council’s decision to hold the March referendum, the group also is suing the city over the council’s separate decision to not put a clean elections program out to voters.

Petitioners gathered more than enough signatures to qualify for a referendum on publicly funded city elections. However, councilors voted to not place the clean elections proposal on the ballot after the city’s top attorney said a mandatory funding provision represents a significant revision of the city charter and would need to be reviewed by a Charter Commission before going to voters.