He changed his surname to
Percy in 1749, nine years after his marriage with
Lady Elizabeth Seymour (1716–1776), daughter of
Algernon Seymour, 7th Duke of Somerset, on 16 July 1740, through a private act of Parliament, the ''''
(23 Geo. 2. c. 14'' ). She was
Baroness Percy in her own right, and indirect heiress of the
Percy family, which was one of the leading landowning families of England and had previously held the
Earldom of Northumberland for several centuries. The title
Earl of Northumberland passed by
special remainder to Hugh Percy, as Elizabeth's husband, when her father died on 7 February 1750; he had been created 1st Earl of Northumberland in 1749. In 1766, the earl was created 1st
Duke of Northumberland and was created
Baron Lovaine on 28 June 1784, with a special remainder in favour of his younger son, Algernon (in reference to the Louvain family of the
Landgraviate of Brabant, which married the Percy heiress, was the origin of the Percy family of England). He was created a
Knight of the Order of the Garter in 1756 and a
Privy Counsellor in 1762. He took a somewhat prominent part in politics as a follower of
John Stuart, 3rd Earl of Bute, and was one of
George III's confidential advisers. He held the office of
Lord Lieutenant of Ireland from 1763 to 1765, and that of
Master of the Horse from 1778 to 1780.
Thomas Chippendale dedicated his ''Gentleman & Cabinet maker's director'' (1754) to him. The Duke and Duchess were prominent patrons of
Robert Adam for
neoclassical interiors in the
Jacobean mansion
Northumberland House, the London seat of the
Earls of Northumberland; it was demolished 1870–1871 to enable the creation of
Trafalgar Square. Remnants of the Northumberland House Glass Drawing-Room are preserved at the
Victoria and Albert Museum. The greater Adam interiors for the Duke are at
Syon House, executed in the 1760s. At
Alnwick Castle, Northumberland, the Duke employed
James Wyatt, whose work has been effaced by later remodellings. One or other Adam designed
Brizlee Tower for the duke. ==Landholdings / seats==