Kirwan was just 18 when he joined the band. At the time the band consisted of Fleetwood, John McVie, Peter Green and Jeremy Spencer.
He was fired in 1972 shortly after the release of the album "Bare Trees."
"Danny's true legacy, in my mind, will forever live on in the music he wrote and played so beautifully as a part of the foundation of Fleetwood Mac, that has now endured over fifty years," Fleetwood said on Facebook. "Thank you, Danny Kirwan. You will forever be missed!"