Mackendrick had a sad and lonely childhood. He attended Hillhead High School from 1919 to 1926 and then went on to spend three years at the Glasgow School of Art. In the early 1930s, MacKendrick moved to London to work as an art director for the advertising firm J. Walter Thompson. Between 1936 and 1938, Mackendrick scripted five cinema commercials. He later reflected that his work in the advertising industry was invaluable, in spite of his extreme dislike of the industry itself. MacKendrick wrote his first film script with his cousin and close friend, Roger MacDougall. It was bought by Associated British and later released, after script revisions, as "Midnight Menace" (1937).