Fleetwood said it was Kiran's "love for the blues" that led him to the band.
According to Variety, no details surrounding his death are immediately available.
"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..."
In the years to follow, the band's founder, Mick Fleetwood, sought the help of the Missing Person Bureau to find Kirwan, claiming he last saw the guitarist in 1980. Fleetwood says in a Facebook post that Kirwan died Friday in London.
Thank you, Danny Kirwan.
His first recorded work reached the US on the 1969 compilation album "English Rose", which included the band's chart-topping United Kingdom instrumental "Albatross" and its B side, Kirwan's composition "Jigsaw Puzzle Blues". You will forever be missed!,' he added.
Back in 2015, during an interview with the New York Observer, Tim Sommer said Kirwan was one of the "great lost figures" in the history of rock music.
Fleetwood later commented in the 1995 film Rock Family Trees: The Fleetwood Mac Story that he did not think Kirwan ever forgave him for the firing.
His most recent work involved three solo albums which were given a belated CD release in February 2006, but only in Japan. The collection was highlighted by Kirwan's rolling composition "Station Man".
He was a key member of the band's late 1960s line-up and was important as a singer and songwriter on the group's albums of the early 1970s. During the decades that followed, he was "reportedly marred by bouts of mental health issues and homelessness". After Welch's departure in 1974, Lindsey Buckingham and Stevie Nicks joined, creating the best-known lineup of the group.
Kirwan was born in Brixton, South London, and his guitar skills started attracting attention at an early age.