Born in Tallinn, Estonia, he studied at the Riga Technical Institute and Moscow University. During the Russian Revolution he supported the counter-revolutionaries and following their failure Rosenberg emigrated to Germany in 1918. He was one of the earliest members of the German Labour Party (later the National Socialist German Workers Party), joining in January 1919, Hitler did not join until October 1919.
Rosenberg became editor of the Völkischer Beobachter, the Nazi party newspaper, in 1921. In 1929 he founded the Militant League for German Culture. He became a Reichstag deputy in 1930 and published his book on racial theory Der Mythus des 20. Jahrhunderts. He was named leader of the foreign political office of the NSDAP in 1933 but played little actual part. In January 1934 he was deputized by Hitler as responsible for the spiritual and philosophical education of the NSDAP and all related organizations. In 1940 he was made head of the Hohe Schule (literally "high school"), the Centre of National Socialistic Ideological and Educational Research. Following the invasion of the USSR Rosenberg was appointed head of the Reich Ministry for the Occupied Eastern Territories. Alfred Meyer was his deputy and represented him at the Wannsee conference
Rosenberg was captured by Allied troops at the end of the war. He was tried at Nuremberg and found guilty of conspiracy to commit crimes against peace; planning, initiating and waging wars of aggression; war-crimes; crimes against humanity. He was sentenced to death and executed with other guilty co-defendants at Nuremberg on the morning of October 16, 1946.
He is considered the main author of key Nazi ideological tenets, including the theory of racism, Lebensraum, abolition of the Versailles Treaty, and persecution of the Jews and Christian churches.