During an extended sojourn in the United States between 1957 and 1960, Nelson received a number of prestigious appointments, serving most notably as a visiting professor at Pratt, Yale, Harvard, and the Massachusetts Institute of Technology, as technical advisor to the U.S. Public Health Service, as a Fellow of the Graham Foundation for Advanced Studies in the Fine Arts, and as a researcher for the Joint Center for Urban Studies at Harvard and MIT. Returning to France, Nelson continued his academic career as professor at the Ecole des Beaux-Arts in Paris and then at the Ecole d'Art et d'Architecture at Luminy, Marseille.
Nelson also nurtured close relationships with major writers, artists, and film figures, including Georges Braque, André Derain, Alexander Calder, Joan Miró and Pablo Picasso. In 1930, Nelson designed the luxurious International Style set for Gloria Swanson's film What a Widow! Among his later commissions was a house for Ferdinand Léger's daughter and a museum for Léger's paintings, both unbuilt. Nelson died in Marseille in 1979.