He served as a Page of Honour at the coronation of King Charles II on 23 April 1661 and on 4 November 1661 entered the Inner Temple for legal training.

[1] On 23 December 1662 he married Lady Elizabeth Wriothesley, 3rd daughter and co-heiress of Thomas Wriothesley, 4th Earl of Southampton,[1] by whom he had children as follows: Following the death of his grandson Algernon Seymour, 7th Duke of Somerset in 1750, the former Percy estates were split between the Smithson (later "Percy", Duke of Northumberland) and Wyndham (Earl of Egremont) families.

[6] The Countess of Northumberland successfully sued for the estates to be returned to the late Earl's only daughter and sole heiress, Lady Elizabeth Percy (1667–1722).

Lady Elizabeth married Charles Seymour, 6th Duke of Somerset (1662–1748), thus forming one of the most wealthy couples in England.

[7] The title Earl of Northumberland was re-created in 1748 for his daughter's son Algernon Seymour, 7th Duke of Somerset (1684–1750), with special remainder to the latter's son-in-law Sir Hugh Smithson, 4th Baronet (1715–1786), later created Duke of Northumberland, who changed his surname to Percy and inherited the ancient Percy seat of Alnwick Castle.