He was the younger son of John Lockhart (Clerk of Petty Sessions at Portrush and Bushmills) and Margaret Lockhart.
In 1911, Margaret Lockhart and her family resided in house 19, Orient Gardens, Cliftonville, Belfast. John has recorded his occupation as a Bank Clerk.
John later joined the Belfast Banking Company and worked in Head Office. Other family at that time included Robert Lockhart of 33 Bedford Street, Belfast and Margery Kate Lockhart of Belfast Bank House, Londonderry.
In April 1913, he passed the final examination of the Institute of Bankers, gaining first place in Ireland and third in the United Kingdom.
In September 1914, Lockhart volunteered and enlisted into 'D Squadron’, North Irish Horse and attained the rank of Lance Corporal. His Service Number is recorded as 1219 with the NIH. Another number, 71288 is recorded with the Corps of Hussars.
This photograph and article appeared in the Coleraine Chronicle in January 1915:
The Belfast Banking Company 'Roll of Honour' booklet describes Lockhart as 'being in hospital' with his last known address as Queenstown.
In 1919 he transferred to the Class Z Army Reserrve.