McMaster was born in Tiruchirappalli in India and later graduated from the University of Edinburgh Medical School[1] with an MD.

[2] He entered the army as an assistant surgeon in March 1855[3] and joined the 78th Highlanders, serving in the Persian War in 1857, before returning with the regiment to India at the beginning of the Indian Mutiny.

[4] McMaster was a 23 years old assistant surgeon in the 78th (Highlanders) Regiment of Foot (later The Seaforth Highlanders) during the Indian Mutiny when the following deed took place on 25 September 1857, at the first relief of Lucknow for which he was awarded the VC: For the intrepidity with which he exposed himself to the fire of the enemy, in bringing in, and attending to, the wounded, on the 25th of September, at Lucknow.

[6] In September 1860 McMaster transferred from the 78th Highlanders to be assistant surgeon of the 6th (Inniskilling) Dragoons,[7] moving to the 18th Hussars in June 1864.

McMaster's widow Eleanor returned to Canada,[1] where she married Canadian surgeon Campbell Mellis Douglas, who had won the VC in the 1867 Andaman Islands expedition.