He was the son of Henry Welbore Ellis, 2nd Viscount Clifden of Gowran and Lady Caroline Spencer daughter of Sir George Spencer, 4th Duke of Marlborough and Lady Caroline Russell.
He married Lady Georgiana Howard, daughter of Sir George Howard, 6th Earl of Carlisle and Lady Georgiana Dorothy Cavendish.
He was a Whig M.P. from 1818-1826 and from 1830 and 1831 and supported Canning's motion in 1822 for a bill to relieve the disabilities of Roman Catholic peers. He was a trustee of the British Museum and a founder of the National Gallery.
F 9784 
Arms: quarterly: 1 and 4, argent on a cross sable five crescents argent; 2 and 3, azure a lion rampant argent.
Crest: a demi-lion rampant.
Supporters: Dexter, a greyhound collarded, the collar charged with three crescents; sinister a lion, with a crest.
Motto: Non hæc sine numine
Lord Dover used 2 other bookplates (F9782, F9783) and another, bearing his title of Lord Dover (after 1831) with Ellis, quartering Agar, impalling Howard (F9775). He also used superlibris stamped on the binding covers of his books see, Binding stamp of George Agar-Ellis, Baron Dover