At the beginning of the 20th century Otto van Rees moved in circles of international modernists (Fauvism, Cubism, Dadaism) and worked with avant-gardists such as Jan Toorop, Kees van Dongen and Jean Arp. Van Rees grew up in an intellectual, socially committed and free-thinking environment. He received his first painting lessons from Jan Toorop and Herman Heijenbrock and initially painted in a neo-impressionist style. In 1904, when he was twenty, he left for Paris on Toorop's advice – closely followed by his girlfriend Catharine (Adya) Duthil, who was a textile artist. He rented a space in the famous Bateau-Lavoir studio building, where he met Braque and Picasso. Van Rees' painting style changed between 1909 and 1912. He left neo-impressionism behind and made way for a more abstract way of working. During this time he was actively involved with Parisian avant-gardists such as Henri Le Fauconnier, Lodewijk Schelfhout, Piet Mondriaan, Fernand Léger and Jacoba van Heemskerck, whom he met at the home of the art critic and painter Conrad Kickert.
During the First World War, Van Rees and Adya, whom he married in 1909, moved to Ascona in Switzerland to settle in the freethinkers' artist colony Monte Verita. Van Rees came into contact with Hans Arp, with whom he and Adya exhibited in a gallery in Zurich in 1915. Adya exhibited embroideries based on avant-garde motifs and Van Rees showed work for which he made collages using materials such as old newspapers, pieces of cigarette packs, cardboard and silver paper. Due to its unconventional nature, the exhibition caused quite a stir and is considered the starting point of Dadaism. However, Van Rees did not continue with this for long. He returned to Paris where he came under the influence of Cubism.
In 1919, Van Rees and his wife left for the Netherlands again, after they were involved in a train accident in France on the way to Ascona, in which their eldest daughter Aditya died. The seriously injured Van Rees was unable to pick up the brush for a year and a half and when he started painting again, the time for experimenting was over. Influenced by painters from the Bergense School, he returned to figuration and focused on painting portraits and French landscapes in a dreamy style.
From 1923 to 1927, Van Rees lived with his family in the Klein Kasteel in Deurne, which he rented from the local general practitioner Hendrik Wiegersma. Van Rees inspired the doctor to develop his artistic talent, with the result that, in addition to a flourishing general practice, he made a name for himself as an expressionist artist. The Klein Kasteel and house 'De Wieger', which Wiegersma had built in 1922, became a meeting place for numerous artists such as Charley Toorop, Jan Sluijters, Leo Gestel, Theo van Doesburg, Jan Mankes and Else Berg.
In the early 1930s, Van Rees joined the group Cercle et Carré in Paris, a group of artists who turned against surrealism. Van Rees again makes cubist work, but now more abstract than he did before. The economic crisis of 1929 had caused the family financial problems and put pressure on the couple's relationship. While Adya lived alternately in Paris and Ascona with her son, Van Rees led an itinerant life.
Through the mediation of his son-in-law, he was given access to a studio in Utrecht in the mid-1930s. There he worked as a designer for the Monthly Journal for Catholic Reconstruction, a cultural magazine for Catholic youth that was published in the office below the studio. In the Utrecht period, Van Rees mainly focused on painting portraits, still lifes and religious scenes.
In the 1950s he traveled again, including to Greece and Yugoslavia. There was a renewed appreciation of his work and in 1956 the Museum of New Religious Art (now the Museum Catharijneconvent) in Utrecht organized a major retrospective exhibition. Van Rees has played an important role in the Dutch art world not only because of his work in which there was much room for experimentation – his oeuvre reflects the developments that occurred in the visual arts from the turn of the last century – but also as an intermediary.