Having attended Mill Hill School,[1] in 1926, he went to Paris to study art history at the Sorbonne and the Institut d'Art et d'Archaeologie; 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.
Upon Focillon's advice, McEwen chose to become a painter rather than a lecturer, which led to a breach with his family, as a result of which he had to support himself financially through painting and picture restoration.
McEwen eventually returned to Paris, where, with Foucillon's assistance, he found a job as an apprentice to an art restorer who worked on collections at the Louvre; soon, he had his own studio and business in the city.
Concurrently, McEwen designed shows of French art in London, and exhibitions of Picasso, Matisse, Braque, Georges Rouault, Léger, and Raoul Dufy followed from 1945 to 1947.
The Picasso show at the Victoria and Albert Museum incited hundreds of letters of protest to The Times of London, which brought the painter great merriment when McEwen translated them for him.
He went to Rhodesia for a month in 1954 for further consultation but found himself unimpressed with what he saw; there was no local artistic scene to speak of, and the avowed intent of the museum's board of directors was to stock its halls with Old Master paintings.
Among the artists whose careers began at the museum were Sam Songo, Mukarobgwa, Boira Mteki, Joseph Ndandarika, John and Bernard Takawira, and Joram Mariga; along with Josia Manzi, Nicholas Mukomberanwa and others, they went on to create one of the first native schools of contemporary art in Africa.
The workshop remained an unofficial part of the museum until its wares began to sell abroad via the efforts of Lord Delaware, David Stirling, and others; eventually the board of directors officially accepted responsibility for its activities.
McEwen left an important bequest to the British Museum, in the form of a collection of specimens in stone, clay and wood (mainly items he had purchased from the artists working in 1957-1973).