Louis LeBel was born on November 30, 1939, in Quebec City, Quebec, the son of Paul LeBel, Q.C., a lawyer, and Marguerite Sasseville. His maternal grandfather was also a lawyer, making Louis the inheritor of a multi-generational legal tradition in Quebec City. He grew up in the provincial capital and was educated in its classical college system.
On August 28, 1965, he married Louise Poudrier (LL.D.), daughter of Louis-Philippe Poudrier and Dorothee Labrie. Louise Poudrier-LeBel went on to become a full professor in the Faculty of Law at Universite Laval, serving on the law faculty from 1972 to 2000 and holding administrative posts including director of the undergraduate program (1974-1975), vice-dean of administration and secretary of the faculty (1993-1995), and vice-dean of teaching (1995-1997). The couple had three children: Paul, Catherine, and Francois.