Brewster grew up in Georgetown, Ontario, where his family moved from Scotland in 1956 when he was six years old. When he was thirteen, his family moved to Guelph, Ontario, where he later attended high school and university. Brewster graduated with a degree in English in 1971 and began working as an editor at Scholastic. As an editor from 1972 to 1984, he was involved with creating Scholastic's Canadian children's publishing program. Brewster was the Editorial Director and Publisher at Madison Press Books between 1984 and 2004.
Brewster's first book for children was Anastasia's Album, which featured Anastasia Romanov, the youngest daughter of Czar Nicholas II, and won the 1996 Silver Birch and Red Cedar Awards. His subsequent books included Inside the Titanic and 882 1/2 Amazing Answers to Your Questions About the Titanic, the latter written with Laurie Coulter. He later collaborated with Coulter to write To Be A Princess, which was nominated for the a Silver Birch and Red Cedar awards. In 2004, the 60th anniversary of D-Day, Brewster's book On Juno Beach, won the Children’s Literature of Canada Information Book Award in 2005. His book, At Vimy Ridge won the Norma Fleck Award in 2008. For the 100th anniversary of the Titanic, Brewster produced a large adult book entitled Gilded Lives, Fatal Voyage in 2012.
- Anastasia's Album (1996)
- The Other Mozart (1997)
- Inside the Titanic (1998)
- To Be a Princess (2002), with Laurie Coulter
- Carnation, Lily, Lily, Rose (2007)
- Breakout Dinosaurs (2007)
- Gilded Lives, Fatal Voyage (2012)
- From Vimy to Victory (2014)