McDonald's first run for public office was during the
1981 provincial election when she was the
Ontario New Democratic Party's candidate in the
riding of
Oriole in
North York. The next year, she entered federal politics and was elected in the
by-election held to fill the vacancy created by
Bob Rae's departure from federal politics to take the leadership of the Ontario NDP. She defeated senior party aide
Gerald Caplan on the third ballot to win the NDP nomination. In the by-election she defeated former
Toronto Sun editor
Peter Worthington, who was running as an
independent, by almost 2,000 votes. In the
1984 federal election, she increased her margin to over 3,500 votes again defeating Worthington who, this time, was running as the official
Progressive Conservative candidate. McDonald championed women's equality both inside and outside Parliament (she was the first Member of Parliament to be addressed as
Ms.) She was a co-founder of the Ontario Committee on the Status of Women, 1971, which lobbied for implementation of the measures of the Report of the Royal Commission on the Status of Women in Canada (to which she had given a brief). As president of the National Action Committee on the Status of Women, in 1980, she gave the organization's brief on equality rights to the Joint Senate-Commons committee on the Charter of Rights. McDonald was also a notable opponent of smoking. She earned the enmity of the
tobacco industry by moving a
private member's bill to restrict smoking and ban tobacco advertising and sponsorships. She succeeded in getting the Non-smokers’ Health Act adopted, as a private member's bill, in 1988, the first legislation in the world to establish smoke-free work and public places. The Bill also would have banned tobacco advertising and sponsorships and regulated sales by listed tobacco products under the
Hazardous Products Act. McDonald's bill was short-listed by a parliamentary committee for debate on the floor of the house and succeeded in winning growing support from MPs from all sides of the House of Commons as health groups lobbied in its favour. On 22 April 1987, ten days prior to the Bill's scheduled
second reading vote,
Health Minister Jake Epp announced the government's intention to introduce a bill that would ban tobacco advertising and sponsorships and strengthen health warnings on cigarette packages. The government also announced that it would prohibit smoking in government buildings and restrict it in other federally regulated workplaces. Despite intense lobbying by the tobacco industry, both McDonald's bill and Epp's Bill C-51, were passed by parliament and given
royal assent on 28 June 1988. The lobbying around McDonald's bill is credited with giving Epp the political motivation to introduce his own legislation. McDonald's bill passed in a
free vote despite the fact that every member of Cabinet present in the House voted against it. McDonald was defeated in the
1988 federal election by
Liberal Dennis Mills by 1,200 votes. She attempted a comeback against Mills in the
1993 federal election, but was defeated by almost 10,000 votes as support for the NDP collapsed nationwide. In 2012, she joined with other Nightingale academics and promoters to form the Nightingale Society. McDonald has since been active on environmental issues, initially with the Campaign for Nuclear Phaseout, and later as co-founder of JustEarth: A Coalition for Environmental Justice, which works on climate change; she was a member of the Board of Directors of Climate Action Network 2010–2014. A co-founder of the Canadian Electoral Alliance, McDonald campaigned for such an alliance for the 2015 federal election, which would lead to adoption of proportional representation at the federal level. McDonald is also a co-founder of the Campaign for the Abolition of Solitary Confinement. She was named a
Member of the Order of Canada in 2015 and elected a Fellow of the Royal Historical Society in 2019. In 2020, she joined with Ryerson academics and supporters to form the Friends of Egerton Ryerson, whose goal is the restoration of Ryerson's reputation and refutation of the false accusations against him. In 2023, she was appointed to the advisory board of the Canadian Institute for Historical Education. ==Writing==