Bertin was born in Altona, Hamburg, Germany, to a Belgian father and a German mother. The family moved to Belgium soon after his birth, where he has resided since with the exception of one year in Germany. He studied languages at the Provincial Trade and Higher Technical Institute in Ghent, after which he initially worked at a bank. He later became a full-time writer. He lives in "Dunwich House" in Gentbrugge. He is the father of actress Brenda Bertin.

Bertin began writing stories at a young age. He published his first science fiction stories at the end of the 1960s, subsequently branching out into horror, his main literary genre, and (in 1984) children's fiction. Much of his work belongs to a cycle of pieces detailing a future history of mankind. Notable among his children's books are the Valentina Hellebel stories, issued in seven books from 1993-2004. He has also written more than forty pulp novels under various pseudonyms and done translations from Dutch to English and English to Dutch. A relatively small portion of his shorter works have been published in English, most of it in the 1970s.

Short stories

• "The City, Dying" (1968)
• "The Whispering Horror" (1968)
• "I Wonder What He Wanted" (1970)
• "Shadows of Fear" (1970)
• "Timestorm" (1971)
• "The Taste of Your Love" (1971)
• "The Ashley Premiere" (1971)
• "My Eyes, They Burn!" (1972)
• "Like Two White Spiders" (1972)
• "Something Ending" (1973)
• "A Pentagram for Cenaide" (1975)
• "Darkness, My Name Is" (1976)
• "Composed of Cobwebs" (1976)
• "The Lover" (1977)
• "Behind the White Wall" (1977)
• "I Hate You" (1977)
• "The Sea is My Bed" (1978)
• "Something Small, Something Hungry" (1978)
• "My Beautiful Darkling" (1979)
• "The Way Back Home" (1979)
• "Never Touching" (1981)
• "The Eye in the Mirror" (2008)

Poetry

• "My House, Full of Shadows" (1970)
• "The Burial of the Hydra" (1970)
• "Waiting for the Dark"

Book reviews

• "Four for Tomorrow by Roger Zelazny" (1973)
• "The Book of Brian Aldiss by Brian W. Aldiss" (1973)
• "Report on Planet Three, and Other Speculations by Arthur C. Clarke" (1973)
• "The Wind from the Sun by Arthur C. Clarke" (1973)
• "Science Fiction: the Great Years by Frederik Pohl and Carol Pohl" (1973)
• "Badge of Infamy by Lester del Rey" (1973)
• "The Sky Is Falling by Lester del Rey" (1973)
• "The Day the Sun Stood Still by Anonymous")1973)
• "Swan Song by Robert R. McCammon" (1988)