Born in 1953 in Gladsaxe, Copenhagen (Denmark), Mr Lars Bay Larsen studied at the Københavns Universitet (University of Copenhagen, Denmark). He graduated in political science in 1976. In 1978, he returned to study at the same university, this time enrolling in the Faculty of Law, where he obtained a law degree in 1983.

After leaving the university, he was appointed as an official at the Danish Ministry of Justice where he worked from 1983 to 1985. From 1985 to 1986, he was Head of Section at the Advokatsamfund (Danish Bar Association). After returning to the Danish Ministry of Justice, he served successively as Head of Section from 1986 to 1991, Head of Division from 1991 to 1995, Head of the Police Department from 1995 to 1999, and Head of the Law Department from 2000 to 2003. During that period, he was also Representative of the Kingdom of Denmark on the K4 Committee from 1995 to 2000, the Schengen Central Group from 1996 to 1998, and the Europol Management Board from 1998 to 2000. He was called to the Bar in Denmark in 1991 and, in 2003, his career turned to the judiciary. At that time, he joined the Højesteret (Supreme Court, Denmark) where he served as a judge until 2006.

Mr Bay Larsen's career also illustrates the fruitful complementarity between practice and teaching, since he was a lecturer from 1984 to 1991 and then, from 1991 to 1996, an associate professor in family law at the Københavns Universitet. Since 2008, he has been a lecturer in European criminal law at the université du Luxembourg (University of Luxembourg).

Judge at the Court of Justice from 11 January 2006 to 7 October 2024. Vice-President of the Court of Justice from 8 October 2021 to 7 October 2024.