By 1960, Van Hoeydonck had established an international reputation, being represented by Denise René and Iris Clert in Paris. He was a member of the 'Zero' group and was a driving force behind the historic exhibition 'Vision in Motion, Motion in Vision' in 1959, featuring alongside Yves Klein, Heinz Mack, Daniel Spoerri, Jean Tinguely and Soto. From a concretely constructed abstraction of reality, purely geometrical structures took form. Movement and light-intervention gradually led him from spatial sensibility to space art during the early 1960s. In 1971 the crew of Apollo 15 placed Van Hoeydonck's Fallen Astronaut on the moon surface, an opportunity granted to the artist that still remains unique today. Van Hoeydonck's ZERO works were included in the landmark exhibition 'ZERO: Countdown to Tomorrow' at the Guggehnheim in New York in 2014-2015.

Van Hoeydonck's works are held by museums worldwide including: Galleria Comunale d'Arte Moderna, Rome; Israel Museum, Jerusalem; Museum of Modern Art, New York; The Solomon R. Guggenheim Museum, New York; Smithsonian Institute, Washington DC; Van Abbemuseum, Eindhoven; Museum Boymans-Van Beuningen, Rotterdam; Walraff-Richartz Museum, Cologne; Koninklijk Museum voor Schone Kunsten, Antwerp; Mu.ZEE, Oostende.