Joni Sledge, center, one of the original members of the music group Sister Sledge, poses with niece Camille Sledge, left, and cousin Amber Sledge in 2006. (Fred Prouser/Reuters)

Joni Sledge, who belonged to the four-sister disco-era group Sister Sledge, best known for its No. 1 hit “We Are Family,” died March 10 at her home in Phoenix. She was 60.

A spokeswoman for the group announced the death but did not disclose the cause.

Ms. Sledge and her sisters, Debbie, Kim and Kathy, formed the Sister Sledge in 1971 in Philadelphia, their home town, but struggled for years before success came.

“The four of us had been in the music business for eight years and we were frustrated,” Joni Sledge told the London Guardian last year. “We were saying: ‘Well, maybe we should go to college and just become lawyers or something other than music, because it really is tough.’ ”

Then they met Bernard Edwards and Nile Rodgers of the hit group Chic, and their breakout soon came. The pair wrote and produced their album “We Are Family,” and soon the women had their first major hit with disco jam “He’s the Greatest Dancer,” which became a top 10 hit in May 1979. (It would sampled years later for Will Smith’s hit “Getting Jiggy Wit It.”)

Joni Sledge, at center, performs with sisters Debbie Sledge and Kim Sledge in 2016. (Larry Busacca/Getty Images for Songwriters Hall Of Fame)

Their biggest hit would come a month later with the title track, an infectious dance anthem that celebrated their familial connection with the refrain, “We are family, I got all my sisters with me.”

While it celebrated their sisterhood, the 1979 hit also became an anthem for female empowerment and unity. It would become their signature hit and was nominated for a Grammy. The song and album sold more than 1 million copies.

The women also had a hit with a cover of the Mary Wells song “My Guy” in 1982 but would never duplicate the success they had in the 1970s. Still, Sister Sledge continued; while sister Kathy left the group for a solo career, the trio of sisters continued to perform and record, including a performance for Pope Francis in 2015.

At the time of the papal event, Kathy released a statement saying she had been barred from participating, citing a “familial dispute that has long been developing between the sisters.”

Joan Elise Sledge was born in Philadelphia on Sept. 13, 1956. Her father, Edwin, was a tap dancer, and her mother, the former Florez Williams, was an actress. The sisters formed their group in Philadelphia in 1971, working first as backup singers.

She is survived by a son, Thaddeus; her sisters; and a half sister.