Tove Jansson was born in Helsinki, Finland, which was then a part of the Grand Duchy of Finland. Her family, part of the Swedish - speaking minority of Finland, was an artistic one: her father Viktor Jansson was a sculptor and her mother Signe Hammarsten - Jansson was a graphic designer and illustrator. Tove's siblings also became artists: Per Olov Jansson became a photographer and Lars Jansson an author and cartoonist.

She studied at University College of Arts, Crafts and Design in Stockholm in 1930 – 33, the Graphic School of the Finnish Academy of Fine Arts in 1933 – 1937 and finally at L'École d'Adrien Holy and L'École des Beaux-Arts in Paris in 1938. She displayed a number of artworks in exhibitions during the 30s and early 40s, and her first solo exhibition was held in 1943.

Tove Jansson wrote and illustrated her first Moomin book, The Moomins and the Great Flood, in 1945, during World War II. She said later that the war had depressed her and she had wanted to write something naïve and innocent. This first book was hardly noticed, but the next Moomin books, Comet in Moominland (1946) and Finn Family Moomintroll (1948), made her famous. She went on to write six more Moomin books, a number of picture books and comic strips. Her fame spread quickly and she became Finland's most widely read author abroad. In 1966 she was awarded the Hans Christian Andersen Award.

Jansson continued painting and writing for the rest of her life, although her contributions to the Moomin series became rare after 1970. Her first foray outside children's literature was Bildhuggarens dotter (Sculptor's Daughter), a semi - autobiographical book written in 1968. After that, she authored five more novels, including Sommarboken (The Summer Book) and five collections of short stories. Although she had a studio in Helsinki, she lived much of her life on a small island called Klovharu, one of the Pellinki Islands near the town of Porvoo. Tove Jansson lived with her female partner, the graphic artist Tuulikki Pietilä.

Jansson is principally known as the author of the Moomin books – stories for children that involve Jansson's creations, the Moomins. They are a family of trolls who are white, round and furry in appearance, with large snouts that make them vaguely resemble hippopotamuses. The first Moomin book, The Moomins and the Great Flood, was written in 1945. Although the primary characters are Moominmamma and Moomintroll, most of the principal characters of later stories were only introduced in the next book, so The Moomins and the Great Flood is frequently considered a forerunner to the main series. The book was not a success (and was the last Moomin book to be translated into English), but the next two installments in the Moomin series, Comet in Moominland (1946) and Finn Family Moomintroll (1948), brought Jansson fame. The original title of Finn Family Moomintroll, Trollkarlens Hatt, translates as "The Magician's Hat".

The style of the Moomin books changed as time went by. The first books, up to Moominland Midwinter (1957), are adventure stories that include floods, comets and supernatural events. The Moomins and the Great Flood deals with Moominmamma and Moomintroll's flight through a dark and scary forest, where they encounter various dangers. In Comet in Moominland, a comet nearly destroys the Moominvalley (some critics have considered this an allegory of nuclear weapons). Finn Family Moomintroll deals with adventures brought on by the discovery of a magician's hat. The Exploits of Moominpappa (1950) tells the story of Moominpappa's adventurous youth and cheerfully parodies the genre of memoirs. Finally, Moominsummer Madness (1955) pokes fun at the world of the theatre: the Moomins explore an empty theatre and perform Moominpappa's pompous hexametric melodrama.

Moominland Midwinter marks a turning point in the series. The books take on more realistic settings ("realistic" in the context of the Moomin universe) and the characters start to acquire some psychological depth. Moominland Midwinter focuses on Moomintroll, who wakes up in the middle of the winter (Moomins sleep from November to April, as mentioned on the back of the book), and has to cope with the strange and unfriendly world he finds. The short story collection Tales from Moominvalley (1962) and the novels Moominpappa at Sea (1965) and Moominvalley in November (1970) are serious and psychologically searching books, far removed from the light - heartedness and cheerful humor of Finn Family Moomintroll.

After Moominvalley in November Tove Jansson stopped writing about Moomins and started writing for adults. The Summer Book is the best known of her adult fiction translated into English. It is a work of charm, subtlety and simplicity, describing the summer stay on an island of a young girl and her grandmother.

Besides the Moomin novels and short stories, Tove Jansson also wrote and illustrated four original and highly popular picture books: The Book about Moomin, Mymble and Little My (1952), Who will Comfort Toffle? (1960), The Dangerous Journey (1977) and An Unwanted Guest (1980). As the Moomins' fame grew, two of the original novels, Comet in Moominland and The Exploits of Moominpappa, were revised by Jansson and republished.

Although she became known first and foremost as an author, Tove Jansson considered her careers as author and painter to be of equal importance. She painted her whole life, changing style from the classical impressionism of her youth to the highly abstract modernist style of her later years. Jansson displayed a number of artworks in exhibitions during the 1930s and early 1940s, and her first solo exhibition was held in 1943. Despite generally positive reviews, criticism induced Jansson to refine her style such that in her 1955 solo exhibition her style had become less overloaded in terms of detail and content. Between 1960 and 1970 Jansson held five more solo exhibitions.

Jansson also created a series of commissioned murals and public works throughout her career, which may still be viewed in their original locations. These works of Jansson's included: The canteen at the Strömberg factory at Pitäjänmäki, Helsinki (1945), The Aurora Children's Hospital in Helsinki, The Kaupunginkellari restaurant of Helsinki Town Hall, The Seurahuone hotel at Hamina, The Wise and Foolish Virgins altarpiece in Teuva Church (1954), A number of fairy - tale murals in schools and kindergartens including the kindergarten in Pori (1984).

In addition to providing the illustrations for her own Moomin books, Jansson also illustrated Swedish translations of classics such as J.R.R. Tolkien's The Hobbit and Lewis Carroll's The Hunting of the Snark and Alice's Adventures in Wonderland (some used later in Finnish translations as well). She also illustrated her late work, The Summer Book (1972).

Tove Jansson worked as illustrator and cartoonist for the Swedish language satirical magazine Garm from the 1930s to 1953. One of her political cartoons achieved a brief international fame: she drew Adolf Hitler as a crying baby in diapers, surrounded by Neville Chamberlain and other great European leaders, who tried to calm the baby down by giving it slices of cake – Austria, Poland, Czechoslovakia, etc. Jansson also produced illustrations during this period for the Christmas magazines Julen and Lucifer (just as her mother had earlier) as well as several smaller productions. Her earliest comic strips were produced for productions including Lunkentus (Prickinas och Fabians äventyr, 1929), Vårbrodd (Fotbollen som Flög till Himlen, 1930), and Allas Krönika (Palle och Göran gå till sjöss, 1933).

The figure of the Moomintroll appeared first in Jansson's political cartoons, where it was used as a signature character near the artist's name. This "Proto - Moomin," then called Snork or Niisku, was thin and ugly, with a long, narrow nose and devilish tail. Jansson said that she had designed the Moomins in her youth: after she lost a philosophical quarrel about Immanuel Kant with one of her brothers, she drew "the ugliest creature imaginable" on the wall of their WC and wrote under it "Kant". This Moomin later gained weight and a more pleasant appearance, but in the first Moomin book The Moomins and the Great Flood (originally Småtrollen och den stora översvämningen), the Immanuel - Kant - Moomin is still perceptible. The name "Moomin" comes from Tove Jansson's uncle, Einar Hammarsten: when she was studying in Stockholm and living with her Swedish relations, her uncle tried to stop her pilfering food by telling her that a "Moomintroll" lived in the kitchen closet and breathed cold air down people's necks.

In 1952, after Comet in Moominland and Finn Family Moomintroll had been translated into English, a British publisher asked if Tove Jansson would be interested in drawing comic strips about the Moomins. Jansson had already drawn a long Moomin comic adventure, Mumintrollet och jordens undergång ("Moomintrolls and the End of the World"), based loosely on Comet in Moominland, for the Swedish language newspaper Ny Tid, and she accepted the offer. The comic strip Moomintroll, started in 1954 in the Evening News, a newspaper for the London area and London commuters (no longer in business). Tove Jansson drew 21 long Moomin stories from 1954 to 1959, writing them at first by herself and then with her brother Lars Jansson. She eventually gave the strip up because the daily work of a comic artist did not leave her time to write books and paint, but Lars took over the strip and continued it until 1975. The series was published in book form in Swedish, and books 1 to 5 have been published in English, Moomin: The Complete Tove Jansson Comic Strip.

Several stage productions have been made from Jansson's Moomin series including a number that Jansson herself was involved in. The earliest production was a 1949 theatrical version of Comet in Moominland performed at Åbo Svenska Teater. In the early 1950s, Jansson collaborated on moomin - themed children's plays with Vivica Bandler, and in 1952 Jansson designed stage settings and dresses for Pessi and Illusia, a ballet by Ahti Sonninen (Radio tekee murron) which was performed at the Finnish National Opera. By 1958, Jansson began to become directly involved in theater as Lilla Teater produced Troll i kulisserna, a play with lyrics composed by Jansson and music composed by Erna Tauro. The production was a success and later performances were held in Sweden and Norway.

In 1974 the first Moomin opera was produced, with music composed by Ilkka Kuusisto.

In 1966 Tove Jansson won the Hans Christian Andersen Award for her contributions to children's literature.

Jansson's Moomin books, originally written in Swedish, have been translated into 33 languages. After the Kalevala and books by Mika Waltari, they are the most widely translated works of Finnish literature. The Moomin Museum in Tampere displays much of Jansson's work on the Moomins. There is also a Moomin theme park named Moomin World in Naantali.

Tove Jansson was selected as the main motif in a recent Finnish commemorative coin, the €10 Tove Jansson and Finnish Children's Culture commemorative coin, minted in 2004. The obverse depicts a combination of Tove Jansson portrait with several objects: the skyline, an artist's palette, a crescent and a sailing boat. The reverse design features three Moomin characters.