Stewart, Edith Helen Vane - Tempest (1879–1959), marchioness of Londonderry , public servant, and hostess, was born 3 December 1879 at Blankney, elder daughter and second among three children of Henry Chaplin , tory MP and cabinet minister, and Lady Florence Chaplin (née Leveson-Gower), daughter of the 3rd duke of Sutherland, the largest landowner in Britain. Her mother died on 10 October 1881 and a good deal of her childhood was spent at the Sutherlands' Scottish home, Dunrobin Castle, under the care of her grandmother. While in London, she lived with her grandparents at Stafford House, later better known as Lancaster House. She appears to have been educated at home. In November 1899, aged 20, she married Charles Stewart Henry (‘Charlie’) Vane-Tempest-Stewart (qv), Viscount Castlereagh, only son of the 6th marquess of Londonderry, who came from one of the richest and most politically powerful families in the kingdom and whose commercial interests included substantial ownership of mines in Co. Durham. Her father-in-law had been lord lieutenant of Ireland (1886–9) and her mother-in-law, Theresa, was sometime president of the Ulster Women's Unionist Council. Her first involvement in political campaigning took place in 1906, when her canvassing and platform speeches helped her husband to be first elected as conservative MP for Maidstone. She was an advocate of women's suffrage but rejected the use of violence to achieve it.
During the first world war, she established the Women's Legion, a quasi-military organisation, which, among other things, made it possible for men engaged in home duties to enter military service. The Legion had several departments, which deployed women in agricultural production, cookery, motor and ambulance driving, dispatch riding, and mechanical and technical work. For this contribution to the war effort, she became the first recipient of the DBE. On the death of her father-in-law (1915), her husband became 7th marquess of Londonderry and she became marchioness. At various times, she was vice-president of the Ulster Women's Unionist Council, chairman of the NI branch of the Institute of District Nursing, and JP in Co. Down and Durham. During the second world war she was an active member of the Red Cross in both Northern Ireland and Durham, and also resuscitated the Women's Legion, which developed a special flying section.
She was well known as a leading hostess, especially at Londonderry House, Park Lane, London, where she established an exclusive dining club, ‘The Ark’, which included, among many others, every British prime minister of the 1930s and the future kings Edward VIII and George VI. She and her husband also regularly entertained in the Londonderrys’ ancestral home in Mount Stewart, Co. Down. Over the years she corresponded with diverse figures from Ireland and abroad such as Michael Collins (qv), Herbert Morrison, Sean O'Casey (qv), Gen. Eisenhower, and the Nazi foreign minister Ribbentrop. In addition, she had a substantial correspondence with Sir Edward Carson (qv) and Ramsay MacDonald. Indeed, when her husband was appointed secretary of state for air (1931–5), he attributed his appointment to his wife's friendship with MacDonald, who was then prime minister. Her friendship with MacDonald was so close that it provoked scurrilous gossip. In 1936–8 the Londonderrys visited the leaders of Nazi Germany on four occasions and entertained Ribbentrop at Mount Stewart. In the Sunday Sun (May 1936) Lady Londonderry wrote an unqualified eulogy of Hitler and the Nazi regime. By 1938 she had changed her mind and become hostile to the Nazis but still appears to have shared her husband's anti-Semitism.
Besides her interest in politics, she loved gardening, and when she and her husband first came to spend considerable time at Mount Stewart she planned a new garden. In the event, some twenty gardeners were employed for this purpose and the garden, regarded by some experts as one of the finest in Europe, was handed over to the National Trust in 1957. She published a number of works which mainly relate to her and her husband's families, including Henry Chaplin, The magic inkpot, and Frances Anne. She also edited, with H. Montgomery Hyde (qv), The Russian journals of Martha and Catherine Wilmot 1803–1808 and More letters from Martha Wilmot, 1819–1829. While never an elected politician, she enjoyed some unique insights into the public life of Britain and Ireland through her extensive correspondence with key political figures of her day, her public service, and her role as a leading hostess. She also enjoyed some political power and influence in her own right from her role in the Ulster Women's Unionist Council and exercised considerable influence over the political career of her husband. Her public support for Nazism in 1936 and the perception that her husband was the most prominent member of the pro-German lobby in Britain clearly tainted the family reputation. After her husband's death in 1949 she seems to have lived exclusively at Mount Stewart, and in the same year she was awarded an honorary LLD from QUB.
She and her husband had four daughters and a son. She was predeceased by her eldest daughter, Lady Maureen Stanley, in 1942 and her only son (the 8th marquess of Londonderry) in 1951. She died at Mount Stewart on 23 April 1959 and was survived by three daughters.