Rondal Partridge was born on September 4, 1917, in San Francisco, California, United States. He had a twin brother named Padraic. His parents were etcher Roi Partridge and photographer Imogen Cunningham. He grew up in a household where he was constantly exposed to the influence of several great California artists of the early 20th century. For example, at the age of four, Rondal Partridge spent time staying at the home of photographer Dorothea Lange and her husband, painter Maynard Dixon. He became so close to Lange that their relationship was often compared to a son's relationship with his mother.