Major General Sir Donald Johnstone McGavin (19 August 1876 – 8 May 1960) was a New Zealand surgeon, army health administrator and medical administrator.
He was born in Chatham, Kent, England.
He qualified as a Doctor of Medicine in 1901.
Johnstone then joined the Royal Army Medical Corps as a civilian surgeon, serving in Natal during the Boer War.
He then moved to New Zealand and started practicing as a surgeon in Wellington, and later became a volunteer medical officer, serving in World War I.
Following the war, he served as Director-General of Medical Services from 1919 to 1924, and as a medical advisor to the Minister of Defence during World War II.
He was knighted in the 1921 Birthday Honours.In 1935, he was awarded the King George V Silver Jubilee Medal.