In 1759, he joined the British Army as a teenager and was a captain of the 85th Regiment of Foot by age 17, an achievement that demonstrated the power of wealth and family standing. He was, nonetheless, a good soldier and fought with distinction in 1759 at the battles of Bergen and Minden. In 1760, he went up to St John's College, Cambridge. Afterwards, he married Lady Anne Crichton-Stuart, daughter of Lord Bute, on 2 July 1764. In 1766, his father was granted a dukedom and he was styled Earl Percy. As a Member of Parliament and the son-in-law of Lord Bute, Percy was promoted to full colonel and appointed an aide-de-camp to the King in 1764, having barely reached his majority. Percy was in chronically poor health from gout and had poor eyesight. He was physically unattractive, being overly thin and having a large nose. Yet, "He was honorable and brave, candid and decent, impeccably mannered, and immensely generous with his wealth."