- "Een Gevaarlijk Man" (1941): This is considered de Spens' most prominent novel, translated in English as "A Dangerous Man." The book presents a suspenseful story of espionage during the Second World War, involving secret agents, clandestine operations, and intrigue.
- "De Gouden Kooi" (1942): Translated into English as "The Golden Cage," this novel tells a story of a young woman searching for personal freedom and fulfillment while grappling with societal expectations and class divisions.
- "De Blauwe Mauritius" (1944): Published in English as "The Blue Mauritius," this book is a detective story set in the world of philately. The protagonist, an art dealer, becomes involved in a mystery surrounding the theft of a rare postage stamp.
- "De Eenzame Man" (1948): Translated as "The Lonely Man," this novel delves into the inner conflicts and emotional turmoil of a protagonist searching for meaning and belonging in the aftermath of the war.
- "De Verborgen Schat" (1950): Published in English as "The Secret Treasure," it's an adventurous novel that takes readers on a treasure hunt with a group of diverse individuals brought together by a shared purpose.
- "De Rode Ridder" (1959): This popular comic book series, created and written by Willy de Spens, features the protagonist Johan, also known as the Red Knight. The series became an enduring part of Belgian comic culture and was later adapted into animation.
- Numerous Short Stories and Articles: De Spens wrote various short stories and contributed to magazines, newspapers, and literary journals throughout his career.