He was in general veterinary practice in Retford, Nottinghamshire. He succeeded his friend and colleague,
John McFadyean, as Professor of Anatomy and Histology at the R(D)VC in 1892. In 1900 he was appointed as the first Principal of the Royal Veterinary College of Ireland at its new premises in Pembroke Road, Dublin. He was editor of the Veterinarian from 1895 until its last edition 1902 and held the George Heriot Research Fellowship in Science in the
University of Edinburgh. Elected President of the RVCS in 1911. He was acknowledged for contributions to embryology and the anatomy of the limbs of the horse and domestic ruminants. With McFadyean and Stockman he was involved in the first experiments to develop the ‘TB’ test in Great Britain.
Life in Ireland In 1911 he was made Lieutenant in the Officer Training Corps (RVCI) and then was promoted to the rank of Provisional Major. The OTC cadets were veterinary students who visited the sick lines of the army veterinary hospitals. Mettam had a dramatic experience in Dublin in April 1916 during the
Easter Rising. The rebels attacked Trinity College Botanic Gardens which was next to Mettam's house and the army, thinking that shots had come from the Principal's house, fired into it, and then entered the house taking Mettam prisoner, he was handcuffed and jailed along with the rebels. He was released, the next day but, in the view of some colleagues, he never fully recovered from the experience. == Death ==