Josh Sumner was born on January 28, 1906. He graduated from the University of Manitoba in 1926 with a Bachelor of Science in Civil Engineering.
Sumner worked for the Royal Canadian Air Force and then, in 1946, he began working for the architectural firm Green Blankstein Russell (GBR). Sumner acted as the director of the engineering and provincial offices for GBR and sat on the Design Committee alongside GBR architects such as David Thordarson and G L Russell. Sumner also did many of the estimates for the firm.