Cornelis graduated in pharmacist, studied in Oxford, UK and received his PhD from the University of Louvain, Belgium in 1974.

He studied antibiotic resistance plasmids in Bristol (UK) and transposons at the University of Freiburg and at the Max Planck Institute in Cologne, Germany.

After his appointment as Professor in Louvain in 1984, he investigated bacterial pathogenesis and joined in 1991 the Christian de Duve Institute in Brussels.

[4][5][6] T3SS is a mechanism by which many bacteria inject a cocktail of toxins, so-called effector proteins into animal, plant or insect cells.

Since 2004, Cornelis also studies Capnocytophaga canimorsus, a bacterium from dog's mouths responsible for fatal infections in humans.