She studied art in Stockholm (1930-33) at Konstfack; at the Helsinki Art Society's drawing school at the Finnish National Gallery (1933-37), and in Paris at Ecole d'Adrien Holy and Ecole des Beaux Arts (1938).   Jansson began her Moomin series in 1945, and drew the comic strip Moomin for the Evening News, London, from 1953 to 1959. 

Jansson has also written adult fiction, short stories and memoirs. Although she became famous with the Moomin characters, Jansson has considered herself first as an artist.  She died in 2001.