In 1985, MacKinnon began drawing weekly cartoons for The Chronicle Herald in Halifax, and was hired full-time in 1986, filling a gap on the paper's editorial page that had been present ever since the retirement of its long-time Cartoonist Bob Chambers in 1976. With the redesign of the Herald's weekend edition in April 2013, his hand-drawn font was used for all the headlines in the "Opinion" section.
Since becoming the paper's regular Cartoonist, MacKinnon has achieved status as one of Canada's finest editorial cartoonists, called by the Canadian Encyclopedia, "among the new breed of distinguished artists" in Canadian editorial cartooning. To date he has won 18 Atlantic Journalism Awards for editorial cartooning, and six National Newspaper Awards (1992, 1993, 2013, 2014 & 2015), including the NNA inaugural Journalist of the Year award for 2014. He came in second in the World Press Cartoon competition in 2004. In 2014 he won the World Press Freedom Award and received their Honourable Mention in 2015. He also won second prize in the 2014 Niels Bugge Cartoon Award. Both a popular and at times controversial Cartoonist, he was named Best Political Cartoonist in Halifax for several years running by The Coast newspaper before it elevated him to their Hall of Fame, thus retiring him from further contest.
Much of MacKinnon's work forms part of the permanent collections of StFX University, the National Gallery of Canada and the Art Gallery of Nova Scotia. In 1996 he was granted an honorary doctorate by St. Mary's University for his work and in 2011 he was made a member of the Order of Nova Scotia. In 2013 he received both an honorary doctorate of fine arts from NSCAD university and the Friend of StFX Award from St. Francis Xavier University. In 2016, he was made a Member of the Order of Canada.
