In August 1750 he was created
Viscount Beauchamp and
Earl of Hertford, both of which titles had earlier been created for and forfeited by his ancestor
Edward Seymour, 1st Duke of Somerset,
Lord Protector of England, following his attainder and execution in 1552. The Seymour family had inherited a
moiety of the
feudal barony of Hatch Beauchamp, in Somerset, by marriage to the heiress Cicely Beauchamp (d.1393). In 1755, according to
Horace Walpole, 4th Earl of Orford, "The Earl of Hertford, a man of unblemished morals, but rather too gentle and cautious to combat so presumptuous a court, was named Ambassador to Paris". However, due to the demands of the French, the journey to Paris was suspended. From 1751 to 1766 he was
Lord of the Bedchamber to
George II and
George III. In 1756 he was made a
Knight of the Garter and, in 1757,
Lord-Lieutenant and Guardian of the Rolls of the County of Warwick and City of
Coventry. From 1759 to 1765, Hertford's household included
Edward Despard, serving his wife as a page. Despard was to hang in London in 1803 as the ringleader of an alleged republican plot against the King. In 1763 Hertford became
Privy Councillor and, from October 1763 to June 1765, was a successful ambassador in Paris. He appointed
David Hume as his Secretary, who wrote of him, "I do not believe there is in the World a man of more probity & Humanity, endowd with a very good Understanding, and adornd with very elegant Manners & Behaviour". He witnessed the sad last months of
Madame de Pompadour, whom he admired, and wrote a kindly epitaph for her. In August 1765 he was appointed
Lord Lieutenant of Ireland. In Dublin, leading representatives of the
Protestant Ascendancy warmly anticipated his arrival. The
Speaker of the
Irish House of Commons,
John Ponsonby, was satisfied that "the public as well as private character of Lord Hertford, together with the great property which he has in Ireland" were "the best securities which we can have for his good behaviour. There could not have been found a person to govern us who in all respects would be so likely to use us well . . .". But with his eldest son,
Francis, Viscount Beauchamp, as his chief secretary, Hertford was in Ireland for just one parliamentary session (October 1765–June 1766). He hastened to return to his court circle in London where he was appointed
Lord Chamberlain 1766–82 (and again April–December 1783). In 1782, when she was only fifty-six, his wife died after having nursed their grandson at
Forde's Farm,
Thames Ditton, where she caught a violent cold. According to Walpole, "Lord Hertford's loss is beyond measure. She was not only the most affectionate wife, but the most useful one, and almost the only person I ever saw that never neglected or put off or forgot anything that was to be done. She was always proper, either in the highest life or in the most domestic." (Walpole visited Forde's Farm on several occasions from his residence at
Strawberry Hill, Twickenham.) Within two years of the tragedy, Lord Hertford had sold Forde's Farm to Mrs Charlotte Boyle Walsingham, and a further two years later, she had re-developed the estate, building a new mansion which she called Boyle Farm, a name still in use today. In July 1793 he was created
Marquess of Hertford, with the subsidiary title of
Earl of Yarmouth. He enjoyed this elevation for almost a year until his death at the age of seventy-six, on 14 June 1794, at the house of his daughter, the
Countess of Lincoln. He died as the result of an infection following a minor injury he received while riding. He was buried at
Arrow, in
Warwickshire. ==Marriage==