Still a teenager, he joined the resistance movement, first as a helper (yatak) and since April 1944 as a fully fledged partisan (partizanin) in the "Avgust Popov" unit.

After the events of September 9, 1944 he studied philosophy at Sofia University and also graduated from the Higher Party School.

Between 1950 and 1959 he served as chief political advisor to Secretary General and Prime Minister Valko Chervenkov, accompanying him on numerous state visits including the first official Bulgarian delegation to the People's Republic of China and the signing of the Warsaw Pact in 1955.

He held numerous high-ranking positions in the state and party nomenklatura, including as director general of the Bulgarian National Radio and Television, head of the departments of Arts and Culture (1966–1968), Propaganda and Agitation (1968–1972) and Trans-border Propaganda (1981–1990) at the Central Committee, chairman of the State Printing Committee at the Council of Ministers (1972–1981).

After his retirement from politics, Krum Vassilev remained a member of the Bulgarian Socialist Party, an occasional columnist and published several books.