Lieutenant General Hargrave entered the Army with a commission as an Ensign on 23rd April 1694 in Viscount Charlemonte’s Regiment of Foot with whom he served in the Low Countries from 1694 - 1696.

A Lieutenant in 1702, he fought in the War of the Spanish Succession and other campaigns against the French and the Spanish. He took part in the expeditions to Cadiz and Vigo in 1702 and was at the relief of Barcelona in 1705 and at the Battle of Almanza in 1707.

Appointed a Brevet Colonel on 15th November 1711, he was present in the Rebellion of 1715 at the battle of Sheriffmuir. He was appointed Colonel of the 31st Regiment on 1st January 1730, transferring to the 9th Foot on 27th January 1737. On 27th August 1739 he became Colonel of The Royal Fusiliers.

He died a Lieutenant General on 21st January 1751 and was buried in Westminster Abbey.