Mary Valentich moved to Calgary from Ottawa in 1976. She worked at the University of Calgary as a sessional instructor before becoming a full-time Associate Professor in the Faculty of Social Work in September 1977. Valentich has served as Assistant, Associate and Acting Dean of the Faculty, as Acting Director of the Gender Institute from 2000-2001, and as Advisor to the President on Women's Issues from 1991-1994. Valentich became an Professor Emerita in 1998.

Throughout her career, Valentich has been active in various organizations and movements related to social justice. She was one of the founding members of the Ottawa and Hull Rape Crisis Centre, and also a founding member of Calgary's first rape crisis centre, later renamed the Calgary Sexual Assault Centre. She has participated annually in "Take Back the Night" walks, and in the commemoration ceremonies for the Montreal Massacre victims, and was "Dr. Mary" on the radio show Hot Talk in the 1990s discussing various aspects of human sexuality. Valentich is a founding member of the Faculty of Social Work's Diversity Committee, the Stop Racism Committee and has been a member of the Social Justice Encounter since inception in 2007.

Valentich is a Certified Sex Educator and Diplomate in Sex Therapy, served on the Board of the Canadian Mental Health Association and Board of Accreditation, Canadian Association of Schools of Social Work. She advocated for gender neutral language in City Council from 1987 to 2010 when the designation of Alderman was officially changed to Councillor. Valentich is also an original member of the Mayor's Committee on Civic Engagement, and a founding member of the Social Workers for Social Justice group.

In 2018, Valentich was chosen by the Canadian Association of Social Workers (CASW) for the Glen Drover Award for Outstanding Service, the highest honour that can be bestowed on a social worker.