Born in Zadar, Dalmatia (then Italy, now part of Croatia), in 1948 he moved to Trieste to attend the Piccolo Teatro di Trieste acting school, and then to Rome to enroll at the National Academy of Dramatic Arts. Garko began his career in the 1950s, playing roles in various genres, especially Westerns and Italian comedies; in recent years he has devoted himself to RAI television films. He portrayed Sartana (together with directors Gianfranco Parolini, and later Giuliano Carnimeo), the protagonist of numerous spaghetti Westerns. In the film "Don Camillo's Comrade" (1965) he played the character Scamoggio, a photographer sent by the party to document the twinning.

Besides the films in which he appeared, he had a varied television career. Among many, we recall his appearance in the television series "Space: 1999" as astronaut Tony Cellini, in the episode titled "Dragon's Domain" (as well as voicing Gwent in the episode "The Infernal Machine" in the same series), and in the television series "Suspects" as industrialist Martin Fischer. From 2002 to 2004 he appeared in the soap opera "Vivere", playing businessman Pierfrancesco Moretti. He took part in a number of commercials; among others, for olive oil, wine and, finally, a medicine together with comedian Fabrizio Fontana from 1995 to 1997. He is currently active mainly as a character actor on television.