After he and his spouse of the time Nina Cassian rallied with the left-wing literary circle Orizont during the late 1940s, Colin started his career as a communist and socialist realist writer. During the early years of the Romanian Communist regime, was assigned offices in the censorship and propaganda apparatus. His 1951 novel Soarele răsare în Deltă ("The Sun Rises in the Delta") was an early representative of local socialist realist school, but earned Colin much criticism from the cultural establishment of the day, for what it perceived as ideological mistakes.
Progressively after the mid-1950s, Colin concentrated on his literary career and emancipated himself from communist ideology. He authored celebrated works such as the mythopoeia Legendele ţării lui Vam ("Legends from Vamland") and fairy tale collections, making his debut in local science fiction literature with Colecţia de Povestiri Ştiinţifico-Fantastice journal. His work in science fiction, culminating in the 1978 novel Babel, earned Colin three Eurocon prizes. He was given posthumous recognition for his contribution to the genre, and an award named in his honor is regularly granted to established Romanian science fiction authors. From 1970 until his death, he was one of the editors for the Writers' Union literary magazine, Viaţa Românească.