| Honorific-Prefix: | The Most Honourable |
| The Marchioness of Londonderry | |
| Birth Name: | Lady Theresa Susey Helen Chetwynd-Talbot |
| Birth Date: | 6 June 1856 |
| Birth Place: | Ingestre Hall, Staffordshire, England |
| Nationality: | British |
| Occupation: | Socialite, political hostess |
| Children: |
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| Parents: | Charles Chetwynd-Talbot, 19th Earl of Shrewsbury Anna Theresa Cockerell |
Theresa Susey Helen Vane-Tempest-Stewart, Marchioness of Londonderry (née Chetwynd-Talbot; 6 June 1856 – 16 March 1919) was a British socialite and political hostess. She was a leading Unionist campaigner against Irish Home Rule, serving as president of the Ulster Women's Unionist Council from 1913 to 1919. She was said to be one of the most "dominating feminine personalities" of the time and was referred to as the "Queen of Toryism" and a "highwaywoman in a tiara."
thumb|left|Lady Theresa Chetwynd-Talbot and her brother, Viscount Ingestre, by Valentine Cameron PrinsepShe was born was born Lady Theresa Chetwynd-Talbot in 6 June 1856 at Ingestre Hall, her family's estate in Staffordshire. She was the elder daughter of Charles Chetwynd-Talbot, 19th Earl of Shrewsbury and his wife Anna Theresa Cockerell (1836–1912). She was brought up with conservative values and was interested in politics. She was an admirer of Benjamin Disraeli.
She married Charles Vane-Tempest, Viscount Castlereagh, later the 6th Marquess of Londonderry, in the private chapel of Alton Hall in 1875. They were both leading Unionist campaigners against Irish independence.[1] She was the President of the Ulster Women's Unionist Council.[2] In 1893, she organised a petition of 20,000 women from Ulster to oppose the 1893 Home Rule bill in parliament.[1]
She was considered the leading Tory hostess and entertained at the couples' houses at Wynyard Park, County Durham, Mount Stewart, County Down, Northern Ireland, and Londonderry House in London. Their guests included royalty.[3] She was said to be one of the "dominating feminine personalities" of the time.[4] She was referred to as the "Queen of Toryism" and a "highwaywoman in a tiara."[2] She was said to be more persuasive than her husband, but they were united in their interests. She was not faithful to her husband.[5]
In 1909 her portrait was made by John Singer Sargent. The painting is now held by the National Trust at Mount Stewart in County Down.[6]
The couple had two sons and one daughter:
Lady Londonderry was widowed in 1915 and died in 1919.[6]