He was born on 20 March 1919 at 81 Thornton Avenue, Streatham, London, the son of John Reynolds Conder, a shipbroker, and his wife Edna Frances, née Benson. Conder's interest in birds began with egg collecting, an activity he later opposed. He was educated at Cranleigh School, Surrey; he won a prize when in the junior school for completing a bird diary, and his basic training in ornithology came through the school ornithological society
When the British expeditionary force was sent to France in 1939 his unit was part of the 51st Highland division, and in June 1940 he was captured at St Valery-sur-Somme. During almost five years' incarceration his interest in ornithology helped him to survive.
He became warden of Skokholm bird observatory and in 1954 he became assistant secretary of the Royal Society for the Protection of Birds (RSPB) at the society's headquarters in London. The Society had a membership of 20,000
When Conder became director in 1963 he appointed specialist staff to deal with nature reserves, research, education, publications, film, and financial administration of the RSB. The competent, enthusiastic team he created built on the opportunities they had, so that when Conder retired thirteen years later membership had risen to over 200,000