Karsh initially planned to become a doctor in his new homeland, but after working for his uncle discovered he had an interest in photography. He gave one of his photographs as a gift to a friend who secretly entered it into a contest. It won first prize. Recognizing his talents, his uncle sent Karsh to apprentice with Boston photographer John H. Garo, whose clientele included famous musicians, artists, journalists and statesmen. It was there that Karsh resolved to photograph “those men and women who leave their mark on the world”.
Karsh returned to Canada and opened his own studio in 1931. He achieved a relatively good reputation establishing an impressive clientele and had photographs published in newspapers across Canada. However, it was not until 1941 that Karsh took a photograph that would change his life. Karsh photographed a scowling and defiant Winston Churchill. The image became a symbol of the spirit of Britain, and one of the most famous photographic portraits in the world. Karsh began to photograph the likes of Albert Einstein, Pope John XXIII, Queen Elizabeth, Pablo Picasso, Helen Keller, Ernest Hemmingway, Joan Miro, Anna Magnani, Elizabeth Taylor and thousands more. His work is held in the permanent collections of the International Photography Hall of Fame and Museum, the Museum of Modern Art, the Metropolitan Museum of Art in New York, the Art Institute of Chicago and many more. The bulk of his work, including more than 260,000 negatives and transparencies, and 50,000 original prints, was sold in 1987 to the National Archives of Canada. He held more than two dozen honorary degrees. Karsh has been the author and subject of many books, including The Faces of Destiny, (1946) In Search of Greatness: Reflections of Yousuf Karsh (1962), Karsh Portfolio (1967), Karsh Portraits (1976) and Karsh: A Fifty-Year Retrospective (1983).