Dyer went to Midleton College, County Cork between 1875 and 1881. In 1885 after his time at the Royal Military College, Sandhurst he joined the Queen's Royal Regiment (West Surrey) as a Lieutenant, and served in riot control duties in Belfast (1886) and the Third Burmese War (1886–87). He then joined the British Indian Army. First joining the Bengal Staff Corps as a Lieutenant in 1887 and being part of the 39th Bengal Infantry, and then joining the 29th Punjabis.