 Haining was commissioned into the Royal Artillery in 1901.He served during the First World War, and after he became a barrister at Lincoln's Inn.After attending the Staff College, Camberley, Haining was appointed Assistant Adjutant and Quartermaster General for 2nd Division based at Aldershot in 1928 and then became a General Staff Officer in 4th Division at Colchester in 1930.