Grant McDonald was born in British Columbia, where he lived and attended school. On the final day of school in June 1940 he enlisted in the Canadian Army where he served for one year before re-enlisting in the Royal Canadian Air Force.
Upon completion of training in Canada, he was posted to the U.K. After further training at Castle Kennedy and Kinlass his crew were posted to RAF St. Eval for anti-submarine sweeps in Whitley Vs.
After conversion to Manchesters and Lancasters, his crew were posted to 44 Squadron commanded by W/E John Nettleton VC.
After a short stay on 44 Squadron, he crew were posted to the newly formed 617 Squadron at RAF Scampton. This Squadron was formed to attack the German Dams. His crew attacked the Sorpe Dam on the night of May 16/17 1943.
His crew left 617 Squadron in early 1944. Grant was posted for instructional duties at 29 OTV Bruntingthorpe before repatriation to Canada in early 1945.