Montgomery County Council member Nancy Floreen will appear on the November ballot as an independent candidate for county executive, the Board of Elections determined Wednesday. (Sarah L. Voisin/The Washington Post)

Nancy Floreen, a longtime Montgomery County Council member who broke from the Democratic Party to run as an independent for county executive, collected enough valid signatures to appear on the ballot this November, ensuring a three-way race for the top position in the left-leaning county.

Floreen submitted 20,360 signatures, of which 13,356 were determined valid, Election Director Margaret Jurgensen wrote Wednesday in a letter to the candidate.

Floreen, a 16-year at-large council member and former mayor of Garrett Park, needed valid signatures from 1 percent of registered voters — 7,243 — to land a spot on the ballot, according to the letter.

She will face Democrat Marc Elrich, a 12-year council member, and Republican Robin Ficker, a lawyer and former state delegate. A Green Party candidate withdrew this month.

While Floreen’s entry into the race to succeed Isiah Leggett (D) can be challenged in court within 10 days, for now, the verification means an upending of political traditions in Montgomery County, where the Democratic primary election has often determined the outcome in November. Democrats outnumber Republicans 3 to 1 in Montgomery, the state’s most populous jurisdiction. But more than a fifth of voters in the county are unaffiliated with any party.

Floreen called Elrich, who is favored by labor unions and progressive groups, and Ficker, who has run for office repeatedly since the 1970s, “flawed extremes” and said she offered a more moderate option that would appeal to a broad array of county residents.

Elrich, who has not accepted campaign contributions from developers, believes they should be held accountable for school crowding and traffic congestion resulting from their projects.

Floreen, whose previous campaigns have benefited from contributions from development and construction interests, is seen as a more palatable candidate by some business leaders.

Ficker is the force behind the successful ballot efforts for term limits and a measure that requires a vote of all nine council members to increase tax revenue beyond the level of inflation.

Floreen, who also served on the county Planning Board, now will begin her formal campaign and plans to open a Rockville campaign office, according to a news release.

“This is a community that needs to move forward and stop having the arguments of the past 30 years — the usual growth and development things,” Floreen said in an interview this week. Voters are “going to see in me some experienced leadership, and they’re going to see in me a vision about how we can advance Montgomery County. How we can grow our tax base and create opportunities for everyone, and at the same time fund our priorities.”

She said she retained two companies and had help from 400 volunteers in collecting the petition signatures.

But Elrich, who served on the Takoma Park City Council before he was elected to the County Council in 2006, said he doubted Floreen had the broad backing she claimed, adding that signatures do not equal support.

He called Floreen’s bid “very different from what people normally do” in county politics.

“It’s one more person competing for votes,” he said. “Normally, all of us accept the results of elections.”

He said his candidacy has “unified” the Democratic Party, which saw a six-way primary race for county executive. Elrich narrowly won the nomination, besting his closest competitor, Potomac businessman David Blair, by 77 votes.

“I think people recognize, despite what some people think, I don’t have any radical plans,” Elrich said. “I don’t have plans to raise taxes; I don’t have plans for some radical agenda. I’m just focused on running the government.”

Ficker, who ran for county executive in 2006 as an independent candidate, called both Elrich and Floreen “two term-limited tax-increase specialists who haven’t improved Montgomery County’s transportation on I-270.”

“To me, they’re two peas in a pod,” Ficker said. “They’ve been there for a decade, and their rhetoric has led the county to decline.”