[2][3] He is also a Professor of European Law at the Katholieke Universiteit Leuven and was a member of the Coudenberg group, a Belgian federalist think tank.

Lenaerts obtained a candidate in law (summa cum laude) in 1974 at the Université de Namur.

He then went on to earn a Master of Laws (LLM) degree at Harvard Law School in 1978, with a Belgian Fulbright scholarship, and a Master in Public Administration (MPA) from the John F. Kennedy School of Government at Harvard University in 1979.

Since 1983, Lenaerts has been Professor of European Law at the Katholieke Universiteit Leuven, since 1990 with the title of buitengewoon hoogleraar.

From 1986 until 1989, he was a Member of the Brussels Bar acting as an attorney in the European Court of Justice, on behalf of the Belgian state.