He was the third child (out of four) of Adriaan Victor Janssen (1854–1942) and Anna Catharina Eelen (1855–1929). He went to high school in Hoogstraten and studied medicine at the Catholic University of Leuven and the University of Ghent.
As part of a family with three siblings, he was the third child of Adriaan Victor Janssen and Anna Catharina Eelen. He attended high school in Hoogstraten before pursuing his medical education at the Catholic University of Leuven and the University of Ghent.