Percy was born on 28 June 1915 in Willesden, London to Polish parents Solomon Levy, a tailor, and Rebecca nee Zeligman. He came from a large family of thirteen children and their father Solomon died in 1921. Percy trained to be a doctor and in 1939 he was working as a medical practitioner at Weymouth and District hospital in Dorset.

Percy was commissioned into the Royal Army Medical Corps at the beginning of the war in 1939. In September 1944, he was attached to HQ Airborne Corps and travelled to the Battle of Arnhem as part of the Operation Headquarters to Nijmegen. As the battle continued it became clear the overstretched Airborne medical personnel needed a relief operation to send more Medical supplies to the Airborne troops in Arnhem. As part of the HQ Medical staff, Percy would accompany Lt Col Herford, a fluent German-speaking Commanding Officer, of 163 Field Ambulance. The relief attempt began in daylight, with the party displaying a Red Cross flag to the south bank of the river. Here they found an abandoned assault boat and paddled across the Rhine.

Their path to Allied positions was unclear, and Privates Bean, Hill, Moore and Keeghan of 163 Field Ambulance were all taken prisoner. Percy is believed to have initially sought refuge, before unsuccessfully attempting to the re-cross the swollen river to Allied positions, swimming the Rhine later in the day.

Percy drowned in the Rhine on 24 September 1944, aged 29 years old. His body was never recovered.