In the 1930s, Masson moved to Spain for two years, where he incorporated Spanish themes and myths, including bullfighting, into his work.lHe soon left when the Spanish Civil War broke out and In 1940, when Paris came under German occupation Masson and his family fled to the US.
During his four years in the United States, his Surrealist ideas found fertile ground and his work was extensively exhibited in New York, and his ideas are said to have significantly influenced the Abstract Expressionists, especially Jackson Pollock, Mark Rothko, and William Baziotes.. This period is also said to be among his most productive, as he discovered Native American history and lore, incorporating relevant motifs and themes in his work. He was also influenced by the collections of Asiatic art at the Museum of Modern Art in New York and Boston’s Museum of Fine Arts, and was introduced to Buddhist philosophy, which permeated his art in the mid-1950s when he began to incorporate forms resembling Chinese and Japanese calligraphy into his art.
Masson returned to France after the end of the war, continuing to work until the late 1970s. Masson's first major retrospective took place at the Baltimore Museum of Art in 1941. In 1958, he participated in the Venice Biennale, which dedicated an entire room to his work. Masson also produced designs for the stage, while his most significant postwar commission took place in 1965 when the novelist and Minister of Cultural Affairs André Malraux invited him to paint the ceiling of the Thétre de l'Odéon in Paris.