The Revenge of the Nerds actor's brother Keith Carradine revealed his sibling took his own life after a "nearly two-decade battle with bipolar disorder", a mental health condition marked by extreme mood changes.
"It is with profound sadness that we must share that our beloved father, grandfather, uncle, and brother Robert Carradine has passed away," Carradine's family said in a statement to Deadline.
"In a world that can feel so dark, Bobby was always a beacon on light to everyone around him.
"We are bereft at the loss of this beautiful soul and want to acknowledge Bobby's valiant struggle against his nearly two-decade battle with bipolar disorder.
"We hope his journey can shine a light and encourage addressing the stigma that attaches to mental illness. "
Keith admitted his brother's condition "got the best of him", but insisted there was "no shame" in mental illness.
Carradine made his movie debut in 1972 film The Cowboys, opposite John Wayne, and he went on to appear alongside Jane Fonda and Jon Voight in Oscar-winning motion picture Coming Home.
As well as starring in Martin Scorsese's Mean Streets in 1973, he appeared opposite his brothers, David and Keith, in Walter Hill's The Long Riders.
Carradine found further fame in 1984 film Revenge of the Nerds, and he played dad Sam McGuire in the 2000s TV series, and 2003's The Lizzie McGuire Movie.
Carradine's half-brother brother, Kill Bill actor David Carradine, died in 2009 aged 72.
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