He was born in Antigonish, Nova Scotia, where he attended high school and later studied arts at St. Francis Xavier University. As a youth he also lived with his family in Kingston, Ontario, and Truro and Halifax, Nova Scotia. He studied Fine Arts at Mount Allison University and graphic design at the Nova Scotia College of Art and Design.
His first paid work as a cartoonist came at the age of 14, when he began drawing a weekly cartoon for The Casket in Antigonish. In high school and university in Antigonish, he drew cartoons for the Antigonish Spectator and the Xaverian Weekly, respectively.
In 1985, MacKinnon began drawing weekly cartoons for the Halifax Chronicle Herald, 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 17 Atlantic Journalism Awards for editorial cartooning, three National Newspaper Awards (1992, 1993 and 2013), and came in second in the World Press Cartoon competition in 2004. In 2014 he won the World Press Freedom Award  and 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.
MacKinnon participated in a panel discussion on political cartooning in Canada at the screening of Cartoonists: Foot Soldiers of Democracy held on March 27, 2015 at the Reel Artists Film Festival. He will appear as a Guest Speaker at Eurocature '15 June 7–11, 2015 in Vienna, Austria.
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. He had not graduated from NSCAD before he began cartooning full-time.
He is married and has two children.
- Inklings: Cartoons and caricatures, 1990
- Inklings II: Cartoons and caricatures, 1994
- Pendemonium: Cartoons & Caricatures, Nimbus, 2002
- Penetration [collected cartoons], Nimbus/Halifax Herald, 2010
- Drawing Opinions: MacKinnon, DeAdder & More: Cartoons and the Stories that Inspire Them, Chronicle Herald, 2013
- Knox, Carsten (2009). "Best Political Cartoonist". The Coast.
- "Bruce MacKinnon". Member Profiles. AAEC. Retrieved 5 May 2013.
- Conrad, Margaret, "The Art of Regional Protest: The Political Cartoons of Donald McRitchie, 1904-1937", Acadiensis, 1991, 29.
- Le Pierrès, Laurent (April 18, 2013). "Bev leaves me holding the bag — full of goodies". Chronicle Herald. Retrieved 12 May 2013.
- "Political Cartoons". Canadian Encyclopedia. Historica-Dominion. Retrieved 5 May 2013.
- DeMont, John (May 1, 2014). "Herald Cartoonist Bruce MacKinnon wins World Press Freedom Award". Chronicle Herald. Retrieved 1 May 2014.
- MacIntyre, Mary Ellen (May 31, 2014). "Bruce MacKinnon Takes Second Place at International Awards Event". Chronicle Herald. Retrieved 1 May 2014.
- Bryant, Nolan. "Snow Packs 'em in at Guelph.".
- "Guest Speakers".
- "Exhibition: Editorial Cartoons". StFX University Art Gallery. Retrieved 1 October 2010.
- "Bruce MacKinnon fonds". Library and Archives Canada. Retrieved 1998.
- "Acquisitions". Art Gallery of Nova Scotia. Retrieved March 1994.
- "StFX to welcome home alumni from North America and Beyond".
- "Bruce MacKinnon, Martha Wilson to get honorary NSCAD degrees". Chronicle Herald. April 29, 2013. Retrieved 5 May 2013.
- "Bruce MacKinnon". Author Bios. Nimbus. Retrieved 5 May 2013.
- Fans of Bruce MacKinnon, Editorial Cartoonist Facebook page
- Editorial cartoonist Bruce MacKinnon on Twitter
- Bruce MacKinnon: Editorial Cartoonist, Jared Matthew Dawe, AMI NewsWatch, 2006 (video)
- Backlash, breakfast, and fans: life as a Herald cartoonist, Kathryn MacDonald, King's Journalism Review, 2011
- MacKinnon Receives Order of Nova Scotia, Corey LeBlanc, The Casket, 2011
- Halifax Cartoonist Chronicles Headline News, Erin Trafford, Global News, 2013
- In Conversation with Bruce MacKinnon, Roger Bill, Bell Aliant on demand, 2013
- Chronicle Herald Wins Seven Atlantic Journalism Awards, Sherri Borden Colley, The Chronicle Herald, 2014.
- Bruce MacKinnon Wins National Award, The Chronicle Herald, 2014.
- Art helps us honour Nathan Cirillo, and try to understand the violence, Peter Simpson, Ottawa Citizen, 2014.
- Halifax cartoonist shares personal connection with War Memorial image Natasha Pace, Global Halifax, 2014.
- Bruce MacKinnon on his touching cartoon Elizabeth Chiu, CTV Atlantic, 2014.
- Bruce MacKinnon's War memorial cartoon touches hearts worldwide Mary Ellen MacIntyre, the Chronicle Herald, 2014.
- Bruce MacKinnon's Cartoon following the tragedy in Ottawa Barry Morgan, The Barry Morgan Show, CJAD, 2014.
- Cpl. Nathan Cirillo’s friend and fellow soldier stoic in preparing for emotional goodbye Steve Maher, Postmedia News, 2014.
- Ottawa shooting: A look back at how the week unfolded Devon Goodsell, CBC News, 2014.
- Ottawa shootings: Bruce MacKinnon's cartoon is the perfect tribute to soldier Nathan Cirillo Adam Withnall, The Independent, 2014.
- Rehtaeh Parsons Cartoon By Bruce MacKinnon Is A Powerful Summation Of A Sad Case (TWEETS) Jesse Ferreras, The Huffington Post, 2014.