Family friend Scott Coopwood said King died on Wednesday due to cancer. He was 68.
King joined the band in 1972 and was part of its first three albums with its distinct three-guitar sound.
He is credited on several of Lynyrd Skynyrd's songs, including Saturday Night Special and Workin' for MCA, and his voice can be heard providing the opening count on Sweet Home Alabama.
"Ed was our brother, and a great songwriter and guitar player," said Gary Rossington, a founding member of the band.
"I know he will be reunited with the rest of the boys in rock and roll heaven."
Rock guitarist Ed King. Source: AAP
King left the band two years before a plane crash killed singer Ronnie Van Zant and guitarist Steve Gaines in 1977.
He rejoined the group 10 years later when it reunited with Johnny Van Zant taking his brother's place, and played with the band until he retired in 1996 due to heart problems.
He had a heart transplant in 2011.
King 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.
Funeral arrangements had not yet been announced on Thursday.
