Educated at Downside School and Magdalene College, Cambridge, Leslie never married or had children. During World War II, he served as an officer in the Irish Guards during the Battle of France before being captured at Boulogne-sur-Mer. He then spent five years in POW camps. After the war, he moved to New York City and later travelled around Europe, settling in Rome. At the age of 78 he returned to his family's homestead, Castle Leslie and travelled to Ibiza for his 85th birthday in 2001. He inadvertently revealed the wedding location of Sir Paul McCartney and Heather Mills by admitting to reporters it was to take place in Castle Leslie, but that it was "a secret". In January 2012, he appeared in the television programme Secrets of the Manor House, which discussed the Leslie family and Castle Leslie, among other manor homes. In 2015, he featured in the TV seriesTales of Irish Castles. Leslie was presented with the Legion d'Honneur at the French embassy in Dublin on 9 November 2015. Leslie survived his older sister, the author Anita Leslie and his younger brother, Desmond Arthur Peter Leslie. The immediate line of succession for the baronetcy are nephew Shaun and nephew Mark. He was a first cousin once removed of former British Prime Minister Sir Winston Churchill as his paternal grandmother, Leonie Jerome, and Churchill's mother, Lady Randolph Churchill, were sisters - the daughters of American financier Leonard Jerome. His mother, Marjorie Ide, was the daughter of Henry Clay Ide, an American former Governor-General of the Philippines. In 2006 he published his autobiography Never A Dull Moment. Leslie died at the age of 99 in April 2016. His nephew Shaun is expected to be recognised as the 5th Baronet once he makes a formal application to be included on the Official Roll.
Family
He was the elder son of Sir John Randolph Leslie, 3rd Baronet, and Marjorie Ide, daughter of General Henry Clay Ide, he was born 6 December 1916 and had an elder sister and an younger brother.
Anita Theodosia Moira Rodzianko King, novelist & biographer; was married to Commander Bill King, World War II submarine commander and yachtsman; had two children.
Desmond Arthur Peter Leslie, pilot, film maker, writer, and musician. Twice married, he had five children.