Born in Kaunas in 1927, he died in Vilnius in 1996. His father was a well-known printer and publisher, his wife Birutė Žilytė is a graphic artist and book illustrator, and his daughter Daina is also a graphic artist. He graduated from the Lithuanian State Art Institute in 1950 with a diploma in graphic art. In 1954, he began to make illustrations for the children’s magazine Genys, and from 1957 he illustrated children’s books (the estimated number is 11 books). He was a member of the Lithuanian Artists’ Union since 1959. In 1964, together with Birutė Žilytė and Laimutis Ločeris, he painted the murals for the Nykštukas children’s cafe in Vilnius. From 1969 to 1972, together with Birutė Žilytė, he painted murals for the Pušelė children’s sanatorium in Valkininkai.
In 1963, he was widely acclaimed as one of the most distinguished Lithuanian children’s book illustrators. That year, Kazys Boruta’s book Jurgio Paketurio klajonės (The Wanderings of Jurgis Paketuris), illustrated by Steponavičius, was published. He soon won recognition outside Lithuania: in 1965 his illustrations for the Lithuanian children’s poet Kostas Kubilinskas’ book Varlė karalienė (The Frog Queen) won him a gold medal at the Leipzig Book Fair, and the Golden Apple at the Bratislava Children’s Book Illustrators’ Biennial in 1967. In 1968, Steponavičius was the first artist from Soviet Lithuania to be invited to improve his skills at the Munich Internationale Jugendbibliothek. In 1989, he won a prize in Lithuania’s Most Beautiful Book Competition, and the Ivan Fiodorov Diploma at the Moscow Book Competition for his illustrations to the book Nemuno šalies pasakos (Tales from the Land of the Nemunas) by the Lithuanian writer Petras Cvirka. This masterpiece was almost ten years in the making: in 1990, the book earned him the National Prize. The influence Steponavičius has had on the revival of book illustration in Lithuania in the 1960s has not yet been fully studied.