Lorenzetti was born in Rafaela, Santa Fe Province, the son of a primary school teacher and a travelling salesman. He studied at the Faculty of Juridical and Social Sciences of the National University of the Littoral, becoming a lawyer in 1978. At the time he counseled several labour unions. He obtained his doctorate in 1983, specializing in private law. Among his first interests was the civil liability of physicians in the exercise of their profession.
Besides his work as a lawyer during 26 years in his native city, he has taught in a number of law faculties around throughout the country. He has dictated hundreds of lectures and published more than 30 books in Argentina and abroad, as well as many articles in specialized publications.
A Doctor in Law and Social Sciences, he is also Doctor Honoris Causa from the University of Litoral, the Northeastern University, the University of Jujuy and the National University of Córdoba. He has been honored as Grand Officer, Order of the Star of Italian Solidarity, by the Italian government. In June 2012 he served as the Co-President of the UNEP World Congress on Justice, Governance and Law for Environmental Sustainability.