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. He joined the 51st Sikhs on 8 March 1914 and in the First World War served in Egypt, Aden, and Mesopotamia. He was promoted to lieutenant on 22 April 1915, to acting captain on 13 April 1916, again on 7 October 1916, and to captain on 22 January 1917. On 1 January 1918 he was awarded the Military Cross. Attending the Staff College, Camberley from 1926 to 1927, he was promoted to major 22 January 1931, Lockhart was brevetted as a lieutenant-colonel on 1 January 1933 and appointed as military attache to the Kingdom of Afghanistan from 10 March 1934 to 1 December 1935. He was Promoted to lieutenant-colonel on 8 November 1936, and was given command of the 1st battalion, the 12th Frontier Force Regiment. He was promoted to colonel on 1 February 1939, and appointed Deputy Director of Staff Duties in the India Office. from 1 February 1939 to 19 December 1939. Promoted to temporary brigadier on 20 December 1939, Lockhart served in the Second World War as Director of Staff Duties in the India Office from 20 December 1939 to 14 December 1941, when he became Military Secretary to the India Office, a position he filled until 9 July 1943. He was promoted to acting major-general on 28 April 1941, to temporary major-general on 28 April 1942, and to the permanent rank of major-general on 24 October 1942. Promoted to acting lieutenant-general on 15 April 1945, he was appointed General Officer CommandingSouthern Command in India that year, and was promoted to lieutenant-general on 23 November. On 19 June 1947, with the independence of India and Pakistan imminent, he was appointed as acting Governor of the North West Frontier Province. 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. He was promoted to general on 1 September. He retired on 1 October 1948, but was recalled to the British forces as Director of Operations during the Malaya Emergency between 1951 and 1952. Retiring in 1951, he served as deputy chief scout for the Boy Scouts Association from 1951 to 1961. He also served on the World Scout Committee of the World Organization of the Scout Movement from 1953 to 1959, and in 1961 was awarded the Bronze Wolf Award, the only distinction of the World Organization of the Scout Movement, awarded by the World Scout Committee for exceptional services to world Scouting. Lockhart died on 11 September 1981, leaving property valued at £4504. His address at death was Gainsborough Nursing Home, 4 Nevil Park, Tunbridge Wells, Kent.