Judge Leonard Łukaszuk was born on 29 September 1930 in Gliny. He graduated from the Faculty of Law and Administration of Warsaw University in 1958. Judge Łukaszuk earned his juris doctor degree in 1968, and a habilitated doctor's degree in 1974. In 1985 he became professor. He headed the Department of International Law and the Chair of International Law of Warsaw University.

He was a member of the Committee on Legal Sciences of the Polish Academy of Sciences and the Commission for Popularisation of International Law-Humanitarian Law of the Central Board of the Polish Red Cross. He is also a member of the Polish Lawyers Association, International Law Association, American Society of International Law, International Association for Philosophy of Law and Social Philosophy.

He is an author of nearly 300 publications, including above 30 books and 8 study books in the field of international law, and law of the sea.

Leonard Łukaszuk was a Judge and Vice-president of the Constitutional Tribunal from 1985 to 1993.