Relatives found Hayes, 65, unconscious in his home next to a still-running treadmill, said Steve Shular, a spokesman for the Shelby County Sheriff's Department.
Paramedics attempted to revive him and took him to a hospital, where he was pronounced dead shortly after 2 p.m., the sheriff's department said.
No foul play is suspected, the agency said in a written statement. Hayes was a longtime songwriter and arranger for Stax Records in Memphis, playing in the studio's backup band and crafting tunes for artists such as Otis Redding and Sam and Dave in the 1960s.
He released his first solo album in 1967, and his 1969 follow-up, "Hot Buttered Soul," became a platinum hit. In 1971, the theme from "Shaft" topped the Billboard Hot 100 for two weeks and won an Academy Award for best original theme song. The song and the movie score also won Grammy awards for best original score and movie theme.
Hayes won a third Grammy for pop instrumental performance with the title track to his 1972 "Black Moses" album. From the late 1990s through 2006, Hayes provided the voice of "Chef" for Comedy Central's raunchy animated series "South Park," as well as numerous songs. The role introduced him to a new generation of fans, but he left after the show lampooned his own religion, the Church of Scientology.
He was inducted into the Rock and Roll Hall of Fame in 2002.
Photo courtesy: WMC-TV, Memphis.