She was a Liberal member of the Legislative Assembly of Ontario, representing the downtown Toronto riding of St. George.
In the 1960 election, she finished first in the ward, entitling her a position on Metro Council in addition to the Toronto seat.
In 1966, she became the second woman[nb 3] to win a seat on the four-member Board of Control and served as the city's budget chief.
Her mayoral campaign focused on an explicitly reformist platform, advocating an end to megaprojects and the adoption of Jane Jacobs-style urbanism as promoted by David Crombie.
St. George had been a staunchly Tory seat for decades, and Campbell faced a prominent opponent in Roy McMurtry, but she was victorious becoming the first woman elected as an Ontario Liberal Party MPP.