Beauclerk was the fourth son of Charles Beauclerk, 1st Duke of St Albans and Diana Beauclerk, Duchess of St Albans. On 12 October 1717, he was given a commission as an ensign in the 31st Regiment of Foot. He fought with the regiment in the Thirteenth siege of Gibraltar in 1727, and in October of that year he was made a captain in the 3rd Regiment of Foot. In May 1735 he transferred to the 1st Foot Guards as a lieutenant colonel.
