Costas Kilaidonis was born in 1940 in Athens, Greece. He was brother of composer and singer Loukianos Kilaidonis (b. 1943). He studied at the Athens School of Fine Arts - ASFA (1958-1962) painting under Panos Sarafianos. He continued his studies at the École Nationale Supérieure des Beaux-Arts in Paris.
Costas Kilaidonis presented the following personal exhibitions: Painting, Nees Morfes Gallery, Athens (1965, 1967). He also participated in the following exhibitions: Panhellenic Exhibition of Young Artists, Zappeion Megaron, Athens (1962, 1964, 1965, 1969, 1973).
Costas Kilaidonis died prematurely of heart failure in 1991 in Athens. He was a member of the Chamber of Fine Arts - EETE.