Gaines was born in Miami, Oklahoma. He began playing guitar after seeing The Beatles in concert as a teenager. His first band, The Ravens, made its first recording at the famous Sun Recording Studio in Memphis, Tennessee. Gaines later played with bands RIO Smokehouse, Rusty Day, Detroit and Crawdad in the 1970s. He also recorded several songs with friend and producer John Ryan that were later released in 1988 by MCA Records as his only solo album, One in the Sun.
In 1976, Gaines' sister, Cassie Gaines, became a member of Lynyrd Skynyrd's female backup singers, The Honkettes. Around the same time, the band was looking for a guitarist to replace Ed King, who left the band the year before. Cassie recommended her brother, and after initial reluctance, the band allowed Gaines to join them onstage for a show. He became a band member within a month, just in time for the recording of Skynyrd's live album One More From The Road.
Gaines' guitar and songwriting skills were a major contribution to the band, as proven on the 1977 album Street Survivors. Three days after the album was released, on October 20, 1977, a plane carrying the band between shows from Greenville, South Carolina to Baton Rouge, Louisiana, crashed outside of Gillsburg, Mississippi; he was 28 years old. The crash killed Ronnie Van Zant, Gaines, his sister Cassie Gaines, assistant road manager Dean Kilpatrick, as well as pilot Walter McCreary and co-pilot William Gray.
Gaines was cremated and buried in Orange Park, Florida in 1977, but was relocated to an undisclosed location after vandals broke into his and bandmate Ronnie Van Zant's tombs on June 29, 2000. Their mausoleums remain as memorials for fans to visit.
- "This is like a start of what I want to do. This is the beginning. I hope that I can be good enough to keep on going... This is all I ever dreamed about, you know? Just doing this." October 17, 1977 interview, the day Street Survivors was released. He was killed three days later by the plane crash.