Born in Zadar, Dalmatia (then Italy, now part of Croatia), he moved to Trieste in 1948 to attend the acting school of the Piccolo Teatro di Trieste, and then to Rome to enter the Accademia nazionale d'arte drammatica. Garko began his career in the 1950s playing roles of various genres, especially in westerns and Italian-style comedies; in his later years he devoted himself to films for RAI television. He gave life to the character of Sartana (together with directors Gianfranco Parolini and later Giuliano Carnimeo), the protagonist of numerous spaghetti-westerns. In the film Il compagno don Camillo (1965) he played the character of Scamoggia, the photographer sent by the party to document the twinning.