Born 30 April 1862, son of Nicholas Mahon of Galway and his wife née Bodkin. A Nicholas Mahon, educated at Queen's College, Galway qualified as LAH Dublin in 1877 and was appointed apothecary to the Ballinrobe Union Workhouse and Co Galway Infirmary; R B Mahon practised for a time at Ballinrobe in the 1890s, while this Nicholas Mahon was still practising there. R B Mahon was educated at St Ignatius College, Galway, and at Queen's College there, a constituent of the old Royal University of Ireland, where he won an exhibition, a junior scholarship, and a senior scholarship in anatomy and physiology. He studied midwifery at the Coombe Hospital in Dublin, and took first place in the first class in medicine at the MD, MCh examination of the Royal University in 1885. After postgraduate study in London, Berlin, Munich, and Bern, he was appointed demonstrator and lecturer in anatomy at Galway, and later demonstrator of anatomy and assistant to the professor of physiology at Cork. During these years he also served as a ship's surgeon in the Allan, Royal Mail, and Booth's North Brazil lines. He practised for a time at Ballinrobe and was medical officer of health for Ballinrobe Union and medical officer to the Infirmary. In 1896 he was clinical assistant at the Eye, Ear, and Throat Hospital at Cork, and in the same year took the English Fellowship though not previously a Member of the College. He then became surgeon to the Central Hospital at Galway, and on the replacement of the Royal University by the National University in 1908 he was appointed professor of the practice of medicine at University College, Galway, and was ultimately awarded the title of professor emeritus. He had the leading practice in the West of Ireland and was a successful teacher. During the first world war he served as a surgical specialist at the Southern Military Hospital, Dartford, Kent, with the rank of captain, RAMC. Mahon was an active member of the British Medical Association: he was president of the Connaught branch in 1923-4, served on the Irish committee 1923-5, and three times, making five years in all, on the Central Council. He was a Fellow of the Royal Society of Medicine and of the Royal Academy of Medicine in Ireland, and a member of the Anatomical Society of Great Britain and Ireland. In 1899 he married Miss Roche, and was survived by their two sons. Professor Mahon died on 21 August 1943, at Nile Lodge, Galway, aged 81. His recreations were fishing, shooting, and golf; and he had travelled widely in Norway, Canada, and North and South America.