Born Konstantin Vasilev Kotsev on June 4, 1926 in the city of Istanbul, he entered the law faculty at the St. Kliment Ohridski University of Sofia where he graduated in 1950. Subsequently, he enrolled acting at The National Academy for Theatre and Film Arts graduating in 1958.

After the graduation, Kotsev was appointed in the Burgas Theatre for a year. In 1959, he joined the troupe of the newly founded Satirical Theatre „Aleko Konstantinov“ in Sofia where he remained until 1984. During the end of the 1980s, Kotsev was part of the Municipal Theatre of Sofia. His film debut in a main role was in 1958 in the Bulgarian film classic On a Small Island directed by Rangel Valchanov. Kotsev has a son Dimitar (born 1971) and a daughter Zornitsa (born 1972).