The crowd running for Philadelphia City Council this primary season is now likely to grow even larger.

Blondell Reynolds Brown, a Democrat who has held an at-large Council seat for five terms, announced Friday that she will not seek a new term this year. That, coupled with the potential retirement of Councilman Bill Greenlee, another at-large Democrat, would create two vacant seats, a tantalizing opportunity in a primary election already teeming with eager and ambitious prospects.

Just seven weeks ago, Brown had said she was planning to seek reelection. In a City Hall news conference Friday, she said she was still struggling with her decision 10 days ago but vowed to remain involved in politics and public policy after her term ends.

“This is not a retirement. In fact, to me, retirement is a four-letter word,” Brown said in a 27-minute speech, after which she declined to answer questions from reporters. “I know there will never be a perfect time. However, this is the right time for me.”

Her departure means another of the 17 Council seats will be up for grabs this year. The crowded May 21 primary could rival or surpass a 40-year record for Council candidates.

A former public-school teacher and professional dancer, Brown serves as Council’s majority whip, the only woman currently in the chamber’s leadership.

On Council, Brown has pushed to require fast-food restaurants to add labels to their menus that disclose nutritional information about their offerings. She advocated for the merger of the Fairmount Park Commission with the city’s Department of Recreation. And she led the fight to pass legislation that required city contractors to disclose demographic data, including gender and race, about their corporate leadership.

Across her five terms, Brown has enjoyed political triumphs and suffered embarrassing stumbles.

She received the most votes in the 2011 primary for at-large Council seats and her popularity helped save then-at-large Councilman Jim Kenney’s career. Kenney, who had angered municipal unions that year, squeaked into the fifth and final Democratic at-large spot with help from joint campaign literature that paired his candidacy with hers.

Two years later, Brown admitted to the city’s Board of Ethics that she had authorized a payment of $3,300 from her political action committee to repay a personal loan from Chaka “Chip” Fattah Jr., son of former U.S. Rep. Chaka Fattah, amid other bookkeeping problems that prompted nearly $50,000 in fines. Her campaign manager, who created a bogus expense report to cover that payment, was later sentenced to a year in federal prison for stealing more than $100,000 from her PAC.

That didn’t quell her popularity with voters. Brown finished second out of five in the 2015 at-large primary, a race in which two other incumbents were voted out of office.