Dr. Frappier is a paediatrician specializing in adolescent medicine, a specialty for which he is a founding member at the Royal College of Physicians and Surgeons of Canada. He is a professor of paediatrics at the Faculty of Medicine of the University of Montreal.

Dr. Frappier is director of the Department of Paediatrics at the University of Montreal and the CHU Sainte-Justine. He was head of section of adolescent medicine (2000-14) and head of the Social Paediatrics at CHU Sainte-Justine. He was president of the Canadian Paediatric Society (2011-12); he is the President of the Assault Prevention Center of Montreal, secretary-treasurer and executive board member of the International Association for Adolescent Health. Dr. Frappier was named Mentor of the Year 2009 for Quebec by the Royal College of Physicians and Surgeons of Canada, and received the award for the excellent work around violence against children, Marie-Vincent Foundation 1999.

His many researches focus on sexuality, sexual assault, eating disorders, and also, especially in marginalized youth, physical and mental health, sexually transmitted infections (STIs) and HIV. He has over 180 articles, book chapters and reports from government or non-governmental agencies. He has organized more than 30 provincial, Canadian, or international scientific conferences. Dr. Frappier has been invited to present on the five continents.