The gift, by Alan Davie, was made after the gallery was able to buy four of his early works with money from the National Heritage Lottery Fund.
He donated 13 oil paintings and 14 gouache drawings, including several works that are of world renown, because he wanted the "cream" to be kept in his native Scotland.
Alan Davie was born in Edinburgh in 1920, and the works donated include his earliest self-portrait, made when he was 17, and some of his famous large abstract oils on canvas.
During the 1950s and 1960s, at the height of his career, he was regarded by many as the European equivalent of American artists Pollock and Mark Rothko, some of whose colourful and powerful abstracts are prominently shown in the Tate Gallery in London, and command vast sums in the international art market.
Mr Davie said yesterday: "It gives me great satisfaction that a major collection of my work will belong to the Scottish National Gallery of Modern Art.
"I have been feted all over the world and it does now seem as if I am becoming more appreciated in my own land.
"In the past, so much of my work has gone abroad, but I have always kept the cream of my work for myself so that it could remain in Scotland."
Patrick Elliott, a curator at the Edinburgh gallery, said: "He is arguably the most important post-war Scottish painter and this is the first time the National Heritage Lottery Fund has been used to buy works by a living artist.
"There aren't that many Scottish artists who are world-renowned, and it will create a lot of local interest.
"He is not only a great artist, but a popular one too. A double whammy for us."
Six of the paintings are on display at the Scottish National Gallery of Modern Art and will remain on show throughout the summer.