Born in the Sanne Parish near Gothenburg in the South of Sweden, Ragnar Sandberg originally planned to be a writer, writing verse and translating Oscar Wilde when he was still at school. He ultimately made the decision to study art and went to Valand Academy of Art in Gothenburg between 1920 and 1925 during which time he travelled a great deal particularly to Fracnce.
Together with his art school contemporary Ivan Ivarson, Sandberg had an exhibition of his work at Galerie Moderne in Stockholm in 1933 and at Göteborgs Konsthall in 1936 but it was not until an exhibition at Svenska franska konstgalleriet followed by an exhibition at Matthieson Gallery in London that his works began to be widely noticed.
Sandberg became recognised as one of Sweden's foremost Colourist painters forming part of the group Gothenburg Colourists.
In 1948, Sandberg moved to Stockholm where he was head of the Swedish Art Academy and in 1958 he was awared an International prize from the Guggenheim Foundation.
In 1952, Sandberg, together with the artists Eric Grate and Carl Kylberg, represented Sweden at the Venice Biennale. A solo exhibition of his work was held at the Gothenburg Art Museum in 1965. Among many of the exhibitions in which his work was included was en exhibition entitled 'Swedish Art' at Wildenstein Gallery in London.