MacKay-Lassonde was a founder of Women in Science and Engineering (WISE) and spoke at the first conference. In 1986, MacKay-Lassonde became the first woman president of the Professional Association of Professional Engineers of Ontario. During that time she created the Canadian Engineering Memorial Foundation in response to the murder of 14 engineering students at her alma mater in 1989. There is a doctoral award named in her honour. She created the "Women in Engineering Advisory Committee" and also chaired the Canadian Engineering Workforce Office. She was particularly involved in ensuring opportunities for women in the engineering profession. In 1987 MacKay-Lassonde ran in the 1987 general election as a Liberal. She was defeated by Margaret Marland who achieved only 599 votes more in retaining her seat.