Born Isabel Mary Bowler in rural Manitoulin Island, Ontario, she moved with her family to the west when she was very young. She grew up on a cattle ranch in Alberta. Paterson's family was quite poor and she had eight siblings. A voracious reader who was largely self-educated, she had brief and informal public schooling during these years: about three years in a country school, from the ages of 11 to 14. In her late teen years, Bowler left the ranch for the city of Calgary, where she took a clerical job with the Canadian Pacific Railway. As a teenager, she worked as a waitress, stenographer, and bookkeeper, working at one point as an assistant to future Canadian Prime Minister R. B. Bennett.