Guinness is born in London to Walter Edward Guinness, 1st Baron Moyne, son of Edward Guinness, 1st Earl of Iveagh, and Lady Evelyn Stuart Erskine, daughter of Shipley Gordon Stuart Erskine, 14th Earl of Buchan. He attends Heatherdown School, near Ascot in Berkshire, followed by Eton College, and Christ Church, Oxford, and is called to the bar in 1931.
As an heir to the Guinness brewing fortune and a handsome, charming young man, Bryan is an eligible bachelor. One of London’s “Bright Young Things,” he is an organiser of the 1929 “Bruno Hat” hoax art exhibition held at his home in London. Also in 1929 he marries the Hon. Diana Mitford, one of the Mitford sisters, and has two sons with her. The couple become leaders of the London artistic and social scene and are dedicatees of Evelyn Waugh‘s second novel Vile Bodies. However, they divorce in 1933 after Diana deserts him for British fascist leader Sir Oswald Mosley.
Guinness remarries happily in 1936 to Elisabeth Nelson, of the Nelson publishing family, with whom he has nine children.
During World War II, Guinness serves for three years in the Middle East with the Spears Mission to the Free French, being a fluent French speaker, with the rank of major. Then in November 1944 Guinness succeeds to the barony when his father, posted abroad as Resident Minister in the Middle East by his friend Winston Churchill, is assassinated in Cairo.
After the war, Lord Moyne serves on the board of the Guinness corporation as vice-chairman (1947-1979), as well as the Guinness Trust and the Iveagh Trust, sitting as a crossbencher in the House of Lords. He serves for 35 years as a trustee of the National Gallery of Ireland and donates several works to the gallery. He writes a number of critically applauded novels, memoirs, books of poetry, and plays. With Frank Pakenham he seeks the return of the “Lane Bequest” to Dublin, resulting in the 1959 compromise agreement. He is invested as a Fellow of the Royal Society of Literature.