Rhys-Davids was born in 1897 to a distinguished family. His father was a professional academic and his mother a prolific author, which afforded the young Rhys-Davids thorough schooling. He showed considerable potential in all subjects and was an excellent student. At the age of 14 Rhys-Davids joined Eton College as a King's Scholar. He gained his School Certificate in July 1913 with higher marks than any other student. In 1914 war had broken out and in mid-1916 Rhys-Davids applied for a commission in the Royal Flying Corps. On 28 August 1916 he reported for training. Rhys-Davids completed his training in the spring of 1917 and was assigned to No. 56 Squadron RFC on 7 March 1917.