Henry Dermot Ponsonby Moore was born on 14 January 1937 in London into an Anglo-Irish aristocratic family, the son of Charles Garrett Ponsonby Moore, 11th Earl of Drogheda, and Joan Eleanor (née Carr).

He was educated at Eton and Trinity College, Cambridge, like his father, before studying painting at Oskar Kokoschka's School of Seeing in Salzburg, Austria.

[2][3] After working briefly as a travel agent in New York City, he took photography lessons from British photographer Bill Brandt.

[2] Then-Viscount Moore (as he was up until inheriting the earldom in December 1989) began his professional career in 1973, with a commission from the American magazine Architectural Digest.

[5][6] He became a leading photographer of architectural interiors and an illustrator of books, and had portraits published in Country Life and Vogue.