Guillet taught high school at the
Eastern High School of Commerce in
Toronto, and later worked as an archivist at the Ontario Archives. Guillet wrote many books about the history of Ontario. Two of his best known books are
Early Life in Upper Canada (1933) and
Pioneer Days in Upper Canada (1933). His book
The Lives and Times of the Patriots, about the 1837
Upper Canada Rebellion, has been extensively referenced by later historians. He also published a study of Ontario taverns and inns. Some of his books, including his 1948 history of the town of Cobourg, are considered "popular histories" and don't specify sources for much of the information. In 1957 Guillet was the editor of
Valley of the Trent, the first of a series of Ontario history books published by the Champlain Society. He wrote a series of papers about Canadian trials, and a short work exploring the death of Canadian painter,
Tom Thomson. Guillet's papers have been preserved in the archives of
Trent University. ==Personal==