Charles Stewart Vane-Tempest-Stewart, 6th Marquess of Londonderry, KG, GCVO, CB, PC, JP, DL (16 July 1852 – 8 February 1915), styled Viscount Castlereagh between 1872 and 1884, was a British Conservative politician, landowner and benefactor, who served in various capacities in the Conservative administrations of the late 19th and early 20th centuries.

A supporter of the Protestant causes in Ulster, he was an opponent of Irish Home Rule and one of the instigators of the formal alliance between the Conservative Party and the Liberal Unionists in 1893.

Gladstone's first Home Rule Bill had just been rejected by parliament and national feelings ran high in Ireland.

According to the Dictionary of National Biography, Londonderry "... filled the viceroyalty with tact and courage, so that when he left Dublin in 1889 the discontent had abated and some measure of prosperity had been restored.

He opposed Gladstone's second Home Rule Bill in 1893 and presided over the meeting which led to the formal political alliance between the Conservatives and the Liberal Unionists.

King Edward VII was a guest at Londonderry's County Durham seat Wynyard Park on five occasions.

[1] In 1903 Londonderry was appointed a Knight Grand Cross of the Royal Victorian Order (GCVO) when Edward VII visited Ireland.

[11] He married Lady Theresa Susey Helen Talbot, daughter of Charles Chetwynd-Talbot, 19th Earl of Shrewsbury, at the private chapel of Alton Hall in 1875.

In a letter dated 13 February 1915 (at Durham County Record Office, in the Londonderry Archive) written from Wynyard Park, the grieving Lady Londonderry wrote to her grandson Robin, Lord Stewart, at his school, as follows: "I was so glad to get your darling little letter...You can imagine what it is for me to lose Darling Pa ["Pa" was Robin's name for his grandfather] - you are so understanding you will know, and you will remember what companions he and I always were.

He moved and opened his eyes even after the doctors thought he was insensible...I should so have loved you to have been in the Chapel Wednesday night and Thursday.