Emily Hobart married Robert Stewart, son of the Irish politician and landowner Robert Stewart, 1st Marquess of Londonderry, in 1794. Her husband used his courtesy title, Viscount Castlereagh, from 1796 until 1821, when he succeeded to the marquessate on his father's death. They were a notably devoted couple but had no children. They did, however, care for the young Frederick Stewart while his father, Charles, Lord Castlereagh's half-brother, was serving in the army. Her devotion to her husband, combined with her love of foreign travel, well equipped Emily for the life of a diplomat's wife, and she was noted for her willingness to accompany her husband abroad, no matter how rigorous the journey.
Husband's suicide
Although there is no doubt that she was concerned by her husband's deteriorating mental condition, which culminated in his suicide in August 1822, she may not have realised quite how serious the matter was. Even days before the suicide she was insisting, in public at least, that while he had been "unwell" he was expected to recover fully. During his last days she was undoubtedly fully aware of his dangerous condition, but was forced to trust in the skill of their doctor, Charles Bankhead. Afterwards she was blamed, perhaps unfairly, by many of his friends and political colleagues for concealing the serious nature of his mental illness: Lord Liverpool, the Prime Minister, in particular accused her of deceiving him about the extent of the problem.
Last years
After her husband's death Emily lived quietly in the country for almost two years. In 1824 she returned to her old social life, arousing the censure of some of her husband's friends who thought her conduct unfeeling. However her health soon failed and she died in 1829.
Social leader
During the Regency of George IV, Lady Castlereagh, along with Lady Jersey, Dorothea Lieven, Lady Cowper, and others, was a Lady Patroness of Almack's, one of the first and most exclusive mixed-gender social clubs in London. In their role as Patroness, they had great influence over the ton, determining social acceptance by designating who might receive "vouchers" to Almack's, thereby setting and enforcing complex, unwritten social codes of the London social elite. Credited with having introduced the quadrille to London, Lady Castlereagh is also remembered for having Almack's doors closed, without exception, at eleven o'clock, even once turning away the Duke of Wellington. Her own parties were considered dull, and her manner was somewhat eccentric: guests described her conversation as an endless flow of trivial information delivered in an oddly detached manner. Despite her frivolous manner, she had been well-educated, and had a passion for literature and music. At their country home, Woollet Hall, North Cray, Lady Castlereagh kept a private zoo, which featured antelopes, ostriches, kangaroos, and a notably bad-tempered tiger. Lady Castlereagh is often mentioned in Regency novels, most famously in Georgette Heyer's Regency romances.
