Sledge, who formed Sister Sledge with her three siblings in 1971, was found unresponsive by a friend at her home in Phoenix, Arizona, her publicist said, reported BBC.
She had not been ill and the cause of death is unknown. Sledge, who is survived by her adult son, last performed with the band in October.
Her death was announced on social media on Saturday - a week before the group were due to perform in Los Angeles.
"Yesterday, numbness fell upon our family," a statement released on Facebook read.
More From This Section
Besides the Grammy-nominated "We Are Family", the hit which sold more than a million copies after it was released in 1978, the group also was known for "He's the Greatest Dancer", "Lost in the Music" and a cover of the Motown classic "My Guy."
They sang "We Are Family" for Pope Francis in 2015.
The Sledge sisters came from a family of performers, including an actress mother, a Broadway star for a father and an opera singer for a grandmother.