The eldest of four brothers, Jock was educated at Fettes College, Edinburgh. In 1905, at the age of eighteen, Jock joined the London Scottish regiment. In 1906 he played in his first rugby international, and during the following two years he was capped ten times as a Scottish International.
In 1908 he left the regiment and went to Madras to seek his fortune. At the outset of war he joined the Madras Volunteers and shipped to Kenya, where he later transferred to the King's African Rifles where he served as a Captain in the 3rd King's African Rifles in the First World War. At the end of the war he managed, with the help of his family, to buy 600 acres of land at Njoro. 
In 1919, at the age of 33, he married sixteen year old Beryl Clutterbuck.
They divorced, date unknown, and he eventually remarried and returned to England.
At the outbreak of the Second World War he rejoined the London Scottish Regiment and achieved the rank of lieutenant colonel. He served in the Ethiopian, North African and Italian campaigns until he was invalided home in 1944. He died in 1945 as a result of the wounds he had received.
Lovell, Mary S.; Straight On Till Morning; the Biography of Beryl Markham. New York: St. Martin's Press, 1987.
"England Births and Christenings, 1538-1975," database, FamilySearch (https://familysearch.org/pal:/MM9.1.1/JQXH-DQX : 30 December 2014, Alexander Buckholm Laidlaw Purves, ); citing Wimbledon, Surrey, England, index based upon data collected by the Genealogical Society of Utah, Salt Lake City; FHL microfilm 994,431.
"England and Wales Census, 1891," database with images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/QN81-Q3Z : 11 December 2017), Alexander L L Purves in household of William L Purves, Wimbledon, Surrey, England; from "1891 England, Scotland and Wales census," database and images, findmypast (http://www.findmypast.com : n.d.); citing PRO RG 12, Surrey county, subdistrict, The National Archives of the UK, Kew, Surrey.