Famous for his work in the scientific sub-field of radio astronomy, Oort is particularly known for his discovery of the rotation of the Milky Way and the accompanying lack of solar centrality within Earth's galaxy. He is also notable for his comet research; his discovery of dark matter; and his identification of the Milky Way's "galactic halo."
After studying physics at Groningen University, he worked at both the Yale Observatory and Leiden University.
He was the 1966 recipient of the Vetlesen Prize and the 1987 winner of the Kyoto Prize.
His marriage to Johanna Maria Graadt van Roggen resulted in sons named Abraham and Coenraad and a daughter named Marijke.
He and American astronomer Edwin Hubble were contemporaries.