Family friend Scott Coopwood said King passed away in Nashville, Tennessee, on Wednesday.
King joined Lynyrd Skynyrd in 1972 when the band had a distinctive three-guitar sound.
He played on their first three albums and is credited with writing several of their songs, including Saturday Night Special and Workin’ For MCA.
His voice can be heard providing the opening count on Sweet Home Alabama.
Gary Rossing, a founding member of the band, said: “Ed was our brother, and a great songwriter and guitar player.
“I know he will be reunited with the rest of the boys in Rock and Roll heaven.”
King left Lynyrd Skynyrd two years before a plane crash killed singer Ronnie Van Zant and guitarist Steve Gaines.
He rejoined the group 10 years later when it reunited with Johnny Van Zant, who took his brother’s place as lead vocalist.
King stayed with the band until 1996 until he retired again due to heart problems.
He was also an original member of the California psychedelic group Strawberry Alarm Clock, which had a hit that King co-wrote called Incense And Peppermints in 1967.