Born in Minnedosa, Manitoba, Canada, Colin Pearson was the youngest child of Ernest William Pearson (1861–1936), a lawyer, and Jessie Pearson, "née" Borland (died 1948). He had one brother, who was killed during World War I, and a sister, who died during childbirth. The family moved to London when Pearson was 7, where he was educated at St. Paul's School. He served with the 5th Battalion, Guards Machine Gun Regiment, at the end of the First World War in 1918, before going up to Balliol College, Oxford as a classical scholar and a Jenkyns exhibitioner. He obtained first-class honours in classical honour moderations (1920) and second-class honours in "literae humaniores" (1922).