Debenjak was born on 8 February 1908 in Kanal ob Soči and died on 26 December 1987 in Ljubljana. He attended grammar school in Ljubljana (1919-1924) and the teachers' college in Tolmin (1924-1925). After his studies he lived for some time with his brother in Novi Sad, where he worked for the railway. From 1930 to 1934 he studied at the Belgrade School of Art and from 1934 to 1937 attended an advanced academic course in painting at the same institution (the class led by Prof. Ljubo Ivanović). From 1937 to 1939 he lived in Paris, where he studied independently at different museums. In 1957 he spent four months in the Paris studio of the graphic artist Johnny Friedlaender on a grant from the Prešeren Fund. Debenjak first became interested in graphic art under the influence of Božidar Jakac when he returned to Ljubljana in 1939. In the 1940s he worked as an illustrator. In 1948-1949 he lectured on graphic art at the School of Arts and Crafts in Ljubljana. From 1950 to his retirement in 1973 he lectured on graphic art at the Ljubljana Academy of Fine Arts. He was a member of several art groups, such as Nezavisni (1954, Belgrade), Xylon (Société Internationale des Graveurs sur Bois, 1953-1960) and Grupa 69 (1969-1973). In addition to the Prešeren Award for lifetime achievement (1960), the Jakopič Award (1974) and the Gottfried von Herder Award (Vienna, 1977), he received an exceptional number of awards for his graphic prints at international exhibitions and biennials: Ljubljana (1957, 1961, 1971, 1973), Tokyo (1957, 1972), Alexandria (1958), Sao Paulo (1959), Zagreb (every two years from 1960 to 1974), Krakow (1968, 1970) and Fredrikstad (1972). He exhibited at two Venice biennials, in 1954 and 1964. In 1977 he donated 500 graphic works to his home town of Kanal ob Soči, where the Riko Debenjak Gallery was founded. Despite the fact that Debenjak focused on graphic art only while he lectured at the Ljubljana Academy of Fine Arts (after retirement, he resumed painting, in which he never moved away from realism), he is the founder of the "Ljubljana school of graphic art", which is a synonym for high-quality modernist graphic art created by the graduates of the Ljubljana Academy of Fine Arts. He was a master of the woodcut, aquatint, etching and lithography. He experimented with colour and different positions of plates. He wrote a manual on graphic art, "Grafika" (1955, reprint 1967). He used stylised motifs from Slovene folk tradition (beehive panels, kneading-troughs and women from Karst) and nature (the sea bottom and tree-bark-resin). With the Magic Dimensions series (1967-1973) he moved to abstraction.
