Although he made nearly 60 films in a 50-year acting career, it is for the two he made with director James Whale that Ernest Thesiger will be best remembered. Born Ernest Frederic Graham Thesiger in London on January 15, 1879, he was the grandson of the first Baron of Chelmsford. Educated at Marlbrough college and the Slade, he originally hoped to become a great painter. Greatness proved elusive, however (though he remained an accomplished watercolour artist), and he quickly turned to the theatre, making his first appearance on stage in a production of "Colonel Smith" in 1909. He put his career on hold when, in 1914, he enlisted as a private in the British army when World War I broke out (he originally hoped to join a Scottish regiment because he wanted to wear a kilt). He did see some action in the trenches but had to be sent home after being wounded (he was quoted afterwards as saying of these experiences, "My dear, the noise! And the people!"). He made his first film appearance in 1916 with The Real Thing at Last (1916) and then returned to the theatre with "A Little Bit of Fluff",' which ran for over 1200 performances and led to him appearing in a film adaptation (A Little Bit of Fluff (1919)).

In 1925 he appeared in Noël Coward's production of "On With the Dance", in which he got to show off his knack for camp performances by playing one of two elderly women sharing a boarding house. In the early 1930s his old friend, actor-turned-director James Whale (who had moved to Hollywood and was enjoying huge success with Frankenstayn (1931)), requested that his friend join him there to play the role of Horace Femm in Whale's upcoming production of The Old Dark House (1932). Thesiger agreed and, along with co-star Eva Moore, stole the film, which became a huge success. He returned to Britain to make The Ghoul (1933) with Boris Karloff. Whale requested Thesiger's services in Hollywood again, this time to appear in his sequel to Frankenstayn (1931), Frankenstayn'ın nişanlısı (1935). Thesiger was given the role of the sinister Dr. Pretorious, after Whale had refused the studio's suggestion of Claude Rains for the role. With help from Whale's direction, some classic dialogue ("Have some gin. It's my only weakness . . .", "To a new world of gods and monsters") and expert camera work (which helped accentuate his skeletal frame), Thesiger stole the show once more. He returned to Britain and, unfortunately, never worked with Whale again. He appeared in the Alexander Korda-produced The Man Who Could Work Miracles (1936) and had a memorable role in the thriller They Drive by Night (1938). He appeared with Will Hay in My Learned Friend (1943) and Don't Take It to Heart! (1944). His other notable films of the 1940s include Henry V (1944) and The Winslow Boy (1948). He returned briefly to America to appear in "As You Like It" on Broadway and afterwards divided his time between theatre and film. Notable later films include Last Holiday (1950) (as Sir Trevor Lampington, discoverer and eponym of Lampington's disease), Laughter in Paradise (1951), Scrooge (1951) and Beyaz Elbiseli Adam (1951) (as an elderly industry magnate). He made his last film appearance in Roma'da bahar (1961) and his last stage performance, opposite Sirs Ralph Richardson and John Gielgud, in a production of "The Last Joke". He passed away shortly afterwards, on the eve of his 82nd birthday, at his home on Gloucester Road in Kensington, London.