Lanctôt began her acting career in 1972, winning an Etrog (now called a Genie) award for best female performance for her starring role in Gilles Carle's La Vrai Nature de Bernadette. Since then, she has appeared in a wide variety of film and television roles, such as Les Corps Célestes (again by Carle); Ted Kotcheff's award-winning The Apprenticeship of Duddy Kravitz, Blood Relatives (by Claude Chabrol) and Guy Fournier's Radio-Canada TV series, Jamais deux sans toi.
She has directed for the theatre also, directing Oleanna by David Mamet for the Théâtre de Quat'Sous in Montreal in 1994, and in 1999, Bousille et les justes by Gratien Gélinas for the Théâtre du Rideau Vert.
She began her live-action film-directing career with L'Homme à tout faire (1980), nominated for best direction and for best film at the Canadian Film Awards in 1981. This success was followed by Sonatine (1983), which launched the career of Pascale Bussières and won both the Genie for best direction at the Canadian Film Awards and the Silver Lion at the Venice Film Festival.
Lanctôt defended Gaétan Soucy's novel La petite fille qui aimait trop les allumettes in the French version of Canada Reads, broadcast on Radio-Canada in 2004.