Karel Zelenko was born in Celje. He studied painting under Professors Martin and Boeckl at the Academy of Fine Arts in Vienna and sculpture at the Academy of Fine Arts in Ljubljana. He graduated under Professor Boris Kalin in 1949. Further, he specialized in graphics under Professor Božidar Jakac (completed in 1951) and in painting under Professor Gabrijel Stupica.
In 1964, he won the Prešeren Fund Award for his graphics exhibited in March 1963 at Mala Galerija in Ljubljana.