Vallman studied at the Royal Institute of Art in Stockholm and developed a colourful naivist style of painting under the influence of Isaac Grünewald and Sven Erixson.

Uno Vallman was one of the original members of the avantgarde movement called COBRA which included artists like Karel Appel and Corneille.

Uno Vallman travelled a lot for studies to for example Italy, Spain, North Africa, China, Rumania, Mexico, Russia and the USA.

In 1968 Uno Vallman was invited to represent Scandinavia together with August Strindberg and Edvard Munch for a modern art exhibition in Mexico City as part of the Olympics.

[3] Uno Vallman also played an interesting role in a story about a painting that he bought at a gallery which was later authenticated to be by the painter Emile Henry Bernard (a friend of Van Gogh, Cézanne and Gaugain.