[1] He returned to Australia to join the public service, but found the fact that his degree was not from an Australian university was a barrier to entry.

David Hay joined the Treasury in 1939, moving to the Department of External Affairs shortly before the start of World War II.

He returned to the public service and was appointed official secretary to the Australian High Commission in Ottawa, Ontario, Canada.

He was appointed Australian Ambassador to Thailand, and played an important role in the early days of the Southeast Asia Treaty Organization (SEATO).

The Department of External Territories was abolished by the Whitlam government in 1973, and Hay was appointed Australia's first Military Ombudsman.