Raised in the United States and England, Loel Guinness was a son of Benjamin Solomon Guinness, a lawyer, from whom he inherited a fortune. He was descended from Samuel Guinness, a Dublin goldsmith (1727-1795), the younger brother of the Guinness brewery's founder Arthur Guinness. In 1940 Loel flew as a fighter pilot in the Battle of Britain, famously buying a petrol station near his aerodrome when his driving was restricted by rationing.
Loel's second wife was Lady Isabel Manners, second daughter of the 9th Duke of Rutland, by whom he had a son, William Loel Seymour Guinness, and a daughter, Serena Belinda ("Lindy"), who married the 5th and last Marquess of Dufferin and Ava, himself the son of Maureen Guinness, one of the famous Guinness Girls. (She was middle daughter of the Hon. Ernest Guinness, himself second son of the 1st Earl of Iveagh, himself third and youngest son of Sir Benjamin Guinness).
Loel's third wife was the socialite Gloria Rubio y Alatorre. Her daughter, Freiien (Baroness) Dolores von Fürstenberg-Herdringen, married Patrick Benjamin Guinness, son of Loel and his first wife Joan Yarde-Buller (and thus a half-brother to the present Aga Khan IV). They had issue, one son, Loel Patrick, and two daughters, Maria Alexandra (married Foulques, Count de Quatrebarbes) and Victoria Christina (who married Philip Niarchos, son of late Greek billionaire Stavros Niarchos).