Justice Dagenais has an undergraduate law degree from the Université de Montréal and a postgraduate law degree from the University of Oxford. She was called to the Quebec bar in 1997 and practised litigation and international arbitration at various law firms before working at Dentons, where she has worked since 2010.
She was a member of the Construction and Infrastructure Section Committee of the Canadian Bar Association and worked as a legal adviser at the Barreau du Québec. Justice Dagenais has spent her career committed to access to justice and has been involved with Justice Pro Bono.