Having joined the Civil Service in 1952, Bloomfield was appointed Permanent Secretary to the power sharing executive in 1974. After the collapse of the executive, he went on to become Permanent Secretary for the Department of the Environment and the Department of Economic Development, and finally Head of the Northern Ireland Civil Service on 1 December 1984. In that capacity he was the most senior advisor to successive Secretaries of State for Northern Ireland and other Ministers on a wide range of issues. He retired from the post in April 1991.