Having attended Mill Hill School, in 1926 he went to Paris to study art history at the Sorbonne and the Institut d'Art et d'Archaeologie; there, his teacher was Henri Focillon.
Through Focillon, McEwen met and befriended artists such as Constantin Brâncuși, Georges Braque, Henri Matisse, Pablo Picasso, and Fernand Léger, and gained a deal of respect for the teachings of Gustave Moreau, which were to influence much of his later career.