"It would be an exaggeration to say I'm not afraid of death, but I'm not afraid of what comes after because I'm not a believer. When I disappear I will disappear, there'll be nothing left," he told the Belgian daily Le Soir just a month ago.
De Duve had decided to commit euthanasia after suffering a fall in his home but was awaiting the arrival of his son from the United States in early May in order to die surrounded by family.
"He left us serenely and refused to take anti-anxiety pills before the final injection. He left with a smile and a good-bye," his daughter Francoise told Le Soir.
De Duve, who studied medicine and chemistry, picked up the 1974 Nobel with fellow Belgian Albert Claude and American George Palade for research on cancer.