She met Rene d'Harnoncourt, her future boss as director of the Museum of Modern Art, while she was working in Washington, D.C., at the Office of the Coordinator of Inter-American Affairs.

[2] She also traveled to Mexico, in 1936, as part of the leftist Committee Against War and Fascism, where she developed an interest in Latin and Central American political graphics.

From 1943 through 1970, Constantine worked in the architecture and design department of the Museum of Modern Art, as associate curator and later as curatorial consultant, where she helped popularize collections that were hard to categorize or had been ignored, which she called "fugitive material".

[2] She organized solo exhibitions for graphic and product designers including Alvin Lustig, Bruno Munari, Massimo Vignelli and Tadanori Yokoo that were described by The New York Times as "career-defining".

Along with Jack Lenor Larsen, Constantine curated wall hangings that toured 11 cities from 1968 to 1969 and wrote Beyond Craft: The Art Fabric in 1973.