[3] Matheson participated in the Battle of Ortona, where an air bursting German shell sent shrapnel into his head and caused damage similar to a stroke.
After the war, Matheson met Edith Bickley, a radiologist's assistant, in St. Anne de Bellevue Hospital in Montreal, Quebec.
A member of the United Church of Canada, Matheson resided in Kingston, Ontario until his death in December 2013.
John Matheson was elected as a Liberal Member of Parliament in the Ontario riding of Leeds in a 1961 by-election.
Matheson was a leading member of the multi-party parliamentary committee whose mandate was to select a new flag design for Canada.
[7] Matheson was portrayed by Peter MacNeill in a Heritage Minute television commercial about his involvement in the Flag committee.
[9] Matheson ruled that 20-year-old Justin Clark, who suffered from cerebral palsy, was mentally competent to make his own decisions and should not be forced into the guardianship of his parents.
The case has been described as "a pivotal moment in the Canadian disability rights movement" and lead to a widespread re-examination of provincial guardianship laws.