He was a New Democratic Party member of the Legislative Assembly of Ontario from 1975 to 1995, and a prominent cabinet minister in the government of Bob Rae.
His son Andrew Mackenzie ran for the Hamilton East seat, but was defeated by Liberal Dominic Agostino.
Following the inconclusive 1985 election, the NDP under Bob Rae allowed the Liberal Party under David Peterson to form a minority government, which lasted for two years.
[8] The NDP won a majority government in the 1990 provincial election, and Mackenzie was appointed as the province's Minister of Labour on October 1 of that year.
[9] In 1992, he helped navigate the passage of Bill 40, which introduced anti-scab provisions during strikes and other positions supported by the labour movement.
Mackenzie also introduced legislation dealing with pay equity for nurses and child-care attendants, and extended unionization rights to farm workers.
Journalist Thomas Walkom recounted the following story in his book, Rae Days: There was some controversy in early 1994 when Mackenzie's son David was hired as a special advisor to the Premier's office.