Born on 1 January 1882 son of Dr A C Horner, he was educated at Tonbridge School, Caius College, Cambridge and St Bartholomew's Hospital. His father had been surgeon and naturalist to two Arctic expeditions before settling down to general practice in Tonbridge, where he was medical officer to Tonbridge School. While at St Bartholomew's Horner was editor of the students' *Journal*, and in 1911 became assistant editor of *The Lancet* until 1915. During the war of 1914-18 he served as a Captain in the RAMC, and afterwards joined the staff of the *British Medical Journal* under Sir Dawson Williams, whom he succeeded in 1928. In May 1941 enemy action destroyed the printing offices of the *BMJ*, which increased the problems of its editor. Latterly his life was overshadowed by ill health and he retired in 1946. He married Grace, daughter of W M Fearon, by whom he had one son; she died in 1950. He died on 7 March 1954.