His mother was Florence Stuart Macgregor, while other ancestors included Bruces, Hamiltons, Cummings, Wallaces and Douglases.

His brother, the diplomat and writer R. H. Bruce Lockhart, claimed that "There is no drop of English blood in my veins.

Lockhart was born 23 June 1893 and educated at the Royal Military College, Sandhurst, and was commissioned onto the Unattached List for the Indian Army as a second lieutenant on 22 January 1913.

[13] He was promoted to colonel on 1 February 1939 (with seniority from 1 January 1936), and appointed Deputy Director of Staff Duties in the India Office.

[10][19] [20] On 19 June 1947, with the independence of India and Pakistan imminent, he was appointed as acting Governor of the North West Frontier Province.

[21] On 15 August 1947, the day British India was partitioned into two independent Dominions, Lockhart was appointed as Commander-in-Chief, Indian Army, with the acting rank of general.