The 'Rhinestone Cowboy' singer has been suffering from memory loss for some time, but told People that physicians only diagnosed him with the neurological disorder six months ago.
Campbell's wife of nearly 30 years, Kim, said that her husband has decided to reveal his illness only because he is planning a final series of concerts this fall, adding: "If he flubs a lyric or gets confused on stage, I wouldn't want people to think, 'What's the matter with him? Is he drunk?'"
Campbell explained that he is using his love of music to cope with the pain and fear that comes with developing a terminal disease.
"I still love performing for my fans. I'd like to thank them for sticking with me through thick and thin," he added.
The musician, whose hits include 'Wichita Lineman' and 'Galveston', has amassed four platinum and six gold albums over the course of his career.
He was inducted into the Country Music Hall of Fame in 2005 and has won eight Grammy awards.
Campbell also famously starred in and performed the theme tune for the 1969 film western True Grit.
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Watch Glen Campbell perform 'Wichita Lineman' below: