In 1938, Trench entered the Colonial Service as a cadet in the British Solomon Islands Protectorate and was seconded to the Western Pacific High Commission in 1941.

From 1939 to 1945, he fought in the Second World War and served in the British Solomon Islands Protectorate Defence Force from 1942 to 1946.

[2] Trench attained the rank of Lieutenant-Colonel in 1947 and studied at the Joint Services Command and Staff College in Swindon, Wiltshire in 1949.

His governorship in Hong Kong inherited from his predecessor an increasingly prosperous city, along with numerous social issues that came with it: water shortages, refugees from mainland China, and an alarming rise in corruption.

After major riots in 1966 and 1967, his administration belatedly introduced some social reforms, including the establishment of City District Offices in 1968 as links between the government and the public; the legislation of an eight-hour work day, six-day work week in 1971; and the introduction of a six-year compulsory primary school education, also in 1971.