John Lowrie Morrison OBE, known as "Jolomo", who studied at the school for five years, will give financial help to the Mackintosh Building fire fund.
He will donate a percentage of his profits from forthcoming exhibitions.
His support comes the day after Hollywood star Brad Pitt and Scots actor and former Art School student Peter Capaldi gave their backing to a £20 million fundraising campaign to restore the structure.
The city and the arts world were rocked on May 23 when flames engulfed the A-listed building.
Around a tenth of the structure and 30% of its contents perished in the blaze.
Jolomo, who studied at the GSA from 1967-72, said he was "devastated" when he heard about the fire.
He said: "I heard the news on radio in my studio. I had to stop painting, I was close to tears.
"The Mack made me who I am, it has a big place in my heart.
"I'm here, a successful artist painting the Scottish landscape, because of all I got from the Mackintosh Building and the people in it.
"The teachers who are there now continue to do that for folks like myself."
He called on other former students to rally round and support the appeal.
Jolomo added: "They will restore the building, and it's up to the alumni to help fund it.
"It has done so much for so many artists over the years, it's time to give something back. People who benefited should be helping out now, even a few pounds adds up."
The painter will donate a percentage of the proceeds from his latest exhibition, Jolomo in the Hebrides, which opens on Saturday at MacGregor Fine Art, in Glasgow's Hope Street.
He has also pledged funds from several other planned exhibitions.
Restoration of the fire-damaged building could cost £20-£35m and take up to four years.
Professor Tom Inns, Director of Glasgow School of Art, said: "We have been overwhelmed by the offers of support that we have received since the fire.
"We are very grateful for this wonderfully generous offer from John Lowrie Morrison, which will help us to ensure that, like him, future generations of students can study and make work in the inspirational Mackintosh Building."
After graduating from GSA, Jolomo worked for 25 years in art education before leaving to paint full-time in 1997.
Celebrities including Sting, Madonna and Rick Stein are among those who have bought his work.
Mr Inns said the school was now beginning to look forward to the hard work which will need to be done to return the Mackintosh Building to its former glory as an inspiring place for students to study and work.
He added: "We have been overwhelmed by the offers of support from around the world since the fire and are hugely grateful to all those people who have donated."
We reported yesterday how actor Pitt and new Dr Who Capaldi are to be trustees of a £20m Art School appeal.
They join Roxy Music singer Bryan Ferry, who became a trustee of Glasgow School of Art more than a year ago.