The Alyth-born singer had been left paralysed from the chest down after an unsuccessful operation on his spine, and he was taken into hospital in early December after suffering a stroke.
His sister, Angie Stewart Hollin, confirmed the folk icon had passed away on December 27.
She wrote online: “It is with deep and profound sadness that I must say that my darling brother, Andy M Stewart has passed away. He died peacefully in hospital on 27th December after a long and brave fight.”
Stewart began to make a name for himself in the group Puddock’s Well, which he co-founded with Dougie Maclean and Martin Hadden, and was invited to join Edinburgh-based band Silly Wizard in the mid-1970s.
With the band, which also featured the likes of Phil Cunningham, Maddy Taylor, the late Johnny Cunningham (elder brother of Phil) and former Rezillos bass player Alastair Donaldson, Stewart released nine records between 1976 and 1988 including the popular Caledonia’s Hardy Sons in 1978 and 1988’s Live Wizardry.
A third live album, simply titled Live Again, was issued in 2012.
Starting out performing at Edinburgh’s legendary Triangle folk club, Silly Wizard’s reputation grew across Europe and the United States, with Stewart’s original compositions Valley of Strathmore and The Queen of Argyll becoming mainstays of the band’s setlists.
When the band broke up in the late 1980s, Stewart regularly performed with Donegal-born guitarist and bouzouki player Manus Lunny, of Capercaillie, and respected Irish folk producer and musician Gerry O’Beirne.
His health deteriorated and he was forced to bring a premature end to his music career.
In 2012, Stewart and Silly Wizard were inducted into the Scots Trad Music Hall of Fame.
Thistle Radio DJ Fiona Ritchie tweeted: “So sad to hear Andy M. Stewart has died. Tremendous voice of Scottish song and great songwriter. Wonderful performer who gave so much. RIP.”
Irish singer Frances Black added: “I’m very sorry and sad to hear of the passing of the amazing Scottish singer songwriter Andy M Stewart, he was a legend.”
And Findlay Napier simply tweeted: “RIP Andy M Stewart. Folk music legend.”