After graduating from Tufts in 1955, McKinnon taught history and government in Weymouth and Holbrook, Massachusetts.

[3] He served as Weymouth's Public Works Commissioner from 1958 to 1963 and was a member of the town's Board of Assessors from 1963 to 1975.

While serving in the senate, he continued teaching American History in the evenings at Quincy Junior College.

[3] In 1987 he was appointed by Governor Michael Dukakis to serve as Chairman of the Massachusetts Turnpike Authority.

During his tenure, Massachusetts had the fewest fatalities on major turnpikes in the United States.