Sir John Randolph Leslie, 3rd Baronet, Anglo-Irish diplomat and writer commonly known as Sir Shane Leslie, is born in Glaslough, County Monaghan, on September 24, 1885. He is a first cousin of Sir Winston Churchill. In 1908, he becomes a Roman Catholic and supports Irish Home Rule.

Leslie is born into a wealthy Anglo-Irish landowning family. His father is Sir John Leslie, 2nd Baronet, and his mother, Leonie Jerome, is the sister of Winston Churchill’s mother, Jennie. Both are daughters of Leonard W. Jerome. His ancestor, The Right Reverend John Leslie, Bishop of the Isles, moves from Scotland to Ireland in 1633 when he is made Bishop of Raphoe in County Donegal and is made Bishop of Clogher in 1661. Bishop Leslie is a vocal opponent of Oliver Cromwell.

Together with his brother Norman, Leslie’s early education begins at home where a German governess, Clara Woelke, is their first teacher. As children the brothers have more contact with servants than they have with their parents. His own daughter, Anita, says, “In my parents’ view schools performed the same functions that kennels did for dogs. They were places where pets could be conveniently deposited while their owners travelled.”

Leslie is educated at Ludgrove School, then Eton College and King’s College, Cambridge. While at Cambridge University he becomes a Roman Catholic and a supporter of Irish Home Rule. He adopts an anglicised Irish variant of his name (“Shane”). Not overly impressed by Eton, as a lower boy he and his roommates occupy “an old, battered warren betwixt the chapel cemetery and Wise’s horse yard … [T]he food was wretched and tasteless … As for thrashings which tyrannised rather than disciplined our house, they were excessive. Bullying was endemic and Irish boys were ridiculed, especially on St Patrick’s Day.”

Leslie refuses to send his own sons to Eton. They are educated at Roman Catholic Benedictine schools: Jack at Downside School and Desmond at Ampleforth College.

In the January 1910 United Kingdom general election Leslie stands as the Irish Parliamentary Party (IPP) candidate for the Londonderry City constituency, losing by just 57 votes. In the second general election later that year he is again narrowly defeated by the Unionist candidate.

Before World War I, Leslie travels extensively and in 1912 he marries Marjorie Ide, the youngest daughter of Henry Clay Ide, then United States ambassador to Spain and former Governor-General of the Philippines. His parents and other family members move temporarily to London at the outbreak of war.

During the war Leslie is in a British Ambulance Corps, until invalided out. He is then sent to Washington, D.C. to help the British Ambassador, Sir Cecil Spring Rice, soften Irish American hostility toward England and obtain American intervention in the war in the aftermath of the 1916 Easter Rising in Dublin and the execution of its leaders. But he also looks to Ireland for inspiration when writing and edits a literary magazine that contains much Irish verse. He becomes a supporter of the ideals of Irish nationalism, although not physical force republicanism.

In the 1918 United Kingdom general election in Ireland, the Irish Parliamentary Party loses massively to Sinn Féin, putting an end to Leslie’s political career, but as the first cousin of Winston Churchill he remains a primary witness to much that is said and done outside the official record during the negotiation of the Anglo-Irish Treaty of 1921. Disappointed, he feels unwanted in Ireland and abandoned by the British. Like many members of the landed gentry from the 1880s who were obliged to turn to other occupations, he can no longer rely on income from landholdings.

Leslie writes extensively, in a wide range of styles, in verse, prose, and polemic, over several decades. His writings include The End of a Chapter (1916), while hospitalised during World War I, The Oppidan (1922), a roman à clef about his life and contemporaries at Eton, an edition of the Letters of Herbert Cardinal Vaughan to Lady Herbert of Lea (1942), and a biography Mrs. Fitzherbert: a life chiefly from unpublished sources (1939), together with an edition of her letters (with Maria Anne Fitzherbert), The letters of Mrs. Fitzherbert and connected papers; being the second volume of the life of Mrs. Fitzherbert (1944). He also writes Mark Sykes: His Life and Letters (1923), a biography of the English traveler, Conservative Party politician and diplomatic advisor. He advises budding novelist Scott Fitzgerald on the title of his first novel, they share correspondence with the future Mnsg. William A. Hemmick, who is Fitzgerald’s teacher at the Newman School.

A passionate advocate of reforestation, Leslie finds the business of running an estate uncreative and boring, and transfers the estate entailed to him to his eldest son, John Norman Leslie, who succeeds as the 4th Baronet. He transfers St. Patrick’s Purgatory on Lough Derg to the Roman Catholic Bishop of Clogher, Eugene O’Callaghan.

The wealth of the Leslies wanes by the 1930s following the Wall Street crash of 1929 and a farm that is loss making. In his unpublished memoirs, Leslie writes “a gentleman’s standing in his world was signalled by his list of clubs and it was worth paying hundreds of pounds in subs.” They continue to maintain their lifestyle, involving attendance at the London season and the entertainment of distinguished visitors, including Anthony Eden at Glaslough. At the outbreak of World War II in 1939 he joins the Home Guard. He spends the remainder of his life between Glaslough and London.

Leslie’s first wife, Marjorie, dies on February 8, 1951. On May 30, 1958, at the Catholic Church of St. Peter & Edward, Westminster, he marries Iris Carola Frazer, who is the daughter of Charles Miskin Laing and Etheldreda Janet Laing.

Leslie dies at the age of 85 at 15b Palmeira Court, Hove, East Sussex, on April 14, 1971. A Requiem Mass is held for him in Westminster Cathedral on October 12, 1971.