In 1973 he received his PhD cum laude with a thesis entitled "Canonical Analysis of Categorical Data" advised by John P. van de Geer.

De Leeuw started his academic career as assistant professor in the Department of Data Theory in Leiden University in 1969.

In 1987 he moved to University of California, Los Angeles, where he became professor of psychology and mathematics, and director of the interdepartmental program in social statistics until 1998.

After his retirement in July 2014 UCLA Statistics started a yearly De Leeuw Seminar series.

His former doctoral students include Willem Heiser,[1] Jacqueline Meulman,[1] Catrien Bijleveld,[1] and Mine Çetinkaya-Rundel.