Horn was born in Athens, on March 9, 1921, the son of theatrical writer Pantelis Horn. He studied in the Drama School of the Royal Theatre (present-day National Theatre) making his theatre debut in 1940. Following that, he worked in the theatre of Marika Kotopouli until 1944 when he established a theatre group with actress Mary Aroni.
In the period 1946 - 1950, Dimitris Horn returned to the Royal Theatre. After a two-year absence abroad, he came back to Greece working with actress Ellie Lambeti. The two formed a great acting partnership until, in 1959, Horn went again on his own.
In the cinema Horn made his mark despite starring in only 10 films. He also starred in weekly shows on the radio and became the Manager of ERT (Greek Radio and Television) in 1974. In 1980, along with his wife, Anna Goulandri, he established the Horn-Goulandri Foundation for the study of Greek civilisation.
Horn died on January 16, 1998 after a long illness.
- Athens by Night - I Athina tin nychta 1962
- Woe to the Young - Alimono stous neous, 1961
- A Thief's First Chance - Mia tou klefti, 1960
- We Have Only One Life - Mia zoi tin echoume, 1958
- The Girl in Black - To Koritsi me ta mavra, 1956
- The Counterfeit Sovereign - Kalpiki lira, 1955
- Windfall in Athens - Kyriakatiko xypnima, 1954
- The Drunkard - Methistakas, 1950
- Applause - Hirokrotimata, 1944
- Voice of the Heart - I Foni tis kardias, 1943