Thomas Evelyn Ellis was born in London in 1880, only son of Frederick George Ellis, 7th Baron Howard de Walden, and Blanche Holden. In 1899 his father died and he became 8th Baron Howard de Walden. In that same year he inherited from his grandmother the Dean Caste Estate near Kilmarnock as well as a large estate in Marylebone, making him one of the richest young men in Britain. In 1917, he changed his surname to Scott-Ellis to perpetuate the name of her family.
Howard de Walden was educated at Eton and then at the Royal Military College, Sandhurst, after which he served as a lieutenant with the 10th Hussars in the Boer War. After leaving the army, he remained an officer with the Territorials and again saw active service during the First World War, attaining the rank of brevet lieutenant-colonel in the Royal Tank Corps.
His London home was at Seaford House, Belgravia, but Howard de Walden was intrigued by the Welsh roots of the Ellis family and from 1911 until 1946 he also rented Chirk Castle near Wrexham. In 1912, he married Margherita van Raalte – who had trained as an opera singer in Paris - and they had five children. The family spent a lot of time at Chirk and became involved in many local activities as well as entertaining friends from London.
Howard de Walden was a great sportsman and was the spare man in the British fencing team at the Intercalated Games at Athens in 1906. He enjoyed sailing and had a passion for horse-racing, being a member of the Jockey Club from 1905 until 1924. He was fascinated by new technology, particularly in his younger years. In 1903 he attempted (unsuccessfully) to build a flying machine. He was more successful with powerboats, then in their infancy, and was heavily involved in the sport in the years before the First World War. He was interested in the development of better engines and was an early exponent of radio communication.
He was also a great patron of the arts and counted many prominent writers, artists and musicians among his friends, entertaining them at his houses in London, Wales and Scotland. He himself wrote several plays and opera librettos – which were not very well received by the critics – and his sponsorship and support were a major influence on the contemporary stage, particularly in Wales.
He was passionate in his interest in the medieval period. Medieval Welsh literature and culture – in particular The Mabinogion – were a major influence on his own writings and he was actively involved in several Eisteddfod. He assembled an important collection of armour at his homes at Kilmarnock and Chirk - and was even found one day eating his breakfast in a full suit of armour in order to prove that well-constructed armour imposed few restrictions on movement. As well as being an excellent swordsman, he was skilled in falconry and hawking. His interest in genealogy and heraldry led him to publish several books on the subject and he was instrumental in the compilation of The Complete Peerage, several volumes of which he co-edited.
Howard de Walden died in London in 1946.