Lépine was born in Montreal, the son of Canadian nurse Monique Lépine, and Algerian businessman Rachid Gharbi. Gharbi was abusive towards and contemptuous of women, and left the relationship when Marc was seven, after Monique returned to nursing to support her children. Lépine and his younger sister lived with other families, seeing their mother on weekends. Lépine was considered bright but withdrawn, and had difficulties with peer and family relationships. He legally changed his name to Marc Lépine at the age of 14 giving "hatred of his father" as the reason.