Robert was born in Kristiania to engineer Ole Christian Olstad and Helene Elisabet Svensson.

Originally born Olstad, his second name Robert was upgraded to surname after an initiative from Chat Noir manager Johan Henrik Wiers-Jenssen.

At Nationaltheatret he played in comedies by Ludvig Holberg, Molière and Noël Coward.

Among his Ibsen characters were "Krogstad" in A Doll's House, "Manders" in Ghosts, and "Begriffenfeldt" and "the button-molder" in Peer Gynt.

He participated in thirteen films, including Trine from 1952, På solsiden from 1956, Fjols til fjells from 1957, Freske fraspark from 1963, and several of the Olsenbanden movies.