Born at Hamua, north of Eketahuna, in 1894, Hopkirk started his scientific career as a cadet in the laboratory of the Biology Department of Victoria University College and in 1912 became a laboratory assistant at the Wallaceville Animal Diagnostic and Research Laboratory.
During World War I, Hopkirk served with the New Zealand Mounted Rifles Brigade in Palestine, reaching the rank of corporal. When he returned from the war, he moved to Australia and attended Melbourne Veterinary School, graduating with a BVSc with first class honours in 1923. He was later awarded the degree of DVSc by the University of Melbourne for his work on bovine mastitis and other animal diseases.
From 1924 to 1945, Hopkirk served in the New Zealand Territorial Force, as an officer in the New Zealand Veterinary Corps. During World War II he was the assistant director of veterinary services for the Central Military District. In 1945 he was transferred to the Reserve of Officers, retiring in 1950. He rose to the rank of major.
Hopkirk became director of the Wallaceville Animal Research Centre in 1923 and would remain in this role until 1945. The bacteriologist Sydney Josland worked under the direction of Hopkirk at the Centre during this period.
Upon his resignation from the Centre in 1945, Hopkirk worked internationally as a senior veterinarian in the United Nations Relief and Rehabilitation Administration. He was a leader of an FAO mission in Ethiopia and later served as veterinary officer for the New Zealand High Commission in London.
On his return to New Zealand, from 1959 until 1961, Hopkirk held a temporary lectureship at Lincoln College.
Hopkirk was president of the New Zealand Veterinary Association on three occasions and was honorary secretary for 12 years and a councillor.
He was a foundation member of the New Zealand Society of Animal Production and in 1967 was elected Fellow of the New Zealand Institute of Agricultural Science. In 1972, Hopkirk was elected an honorary member of the New Zealand Microbiological Society.
- "Hopkirk, Cyril Spottiswoode Moy – WWI 50737, WWII N/N – Army". Archives New Zealand. Retrieved 18 January 2015.
- "Hopkirk, Cyril Spottiswoode Moy – WW1 50737 – Army". Archives New Zealand. Retrieved 18 January 2015.
- Transactions of the Royal Society of New Zealand. Royal Society of New Zealand. 62: 23. 1931. Missing or empty
- Annual report. New Zealand Department of Agriculture. 1946. p. 22.
- New Zealand agricultural science. New Zealand Institute of Agricultural Science. 1–3: 53. 1965. ISSN 0549-0146. Missing or empty
- "C. S. M. Hopkirk". New Zealand journal of dairy science and technology. New Zealand Dairy Research Institute. 7–9: 122. 1972. ISSN 0300-1342.
- "No. 43856". The London Gazette (Supplement). 1 January 1966. p. 42.