Born 7 October 1871 at Brightley, Umberleigh, North Devon, the second son of John Mortimer, yeoman, and his wife Mary Graddon. He was educated at Blundell's School, Tiverton, and at the London Hospital, where he was first Buxton scholar in 1890. He took the Conjoint qualification in 1895, and proceeded to London graduation in medicine, 1896, and in surgery, 1897. He served as senior assistant house surgeon at Poplar Hospital and as house surgeon at the London Hospital. In 1906 he took the Fellowship. After a period in British Honduras, where he served as assistant colonial surgeon, he came back to Devonshire and practised at Hatherly House, South Molton, North Devon. He was for some years medical officer of health for the South Molton Rural District. Mortimer married in 1899 Beatrice Mary Wilders, who survived him with a daughter. He died at Moledown, South Molton on 3 July 1946.