Ernest was the second son of brewing magnate Edward Guinness, 1st Earl of Iveagh, and his wife Adelaide.

[1] Ernest and Marie Clothilde had: Ernest was seen as the modernising technical expert among the Guinness family directors at Guinness from 1900 to the 1930s, until he was seriously injured in a motorboat accident at sea in Killary lough.

A keen motorist, he bought a custom-built V16 Cadillac, from Mayfair dealer Lendrum & Hartman Limited which was exhibited at 1930 London Motor Show.

In 1934 he was involved in building a new brewery at Park Royal in the suburbs of London.

He was educated at Trinity College, Cambridge, served with the London Rifle Brigade and as a Deputy Lieutenant and a Justice of the peace for County Dublin.