Catharine was the older sister of Susanna Moodie. She began her carreer writing children's books, publishing 12 before her marriage in 1832, often on the benefits of obedience to one's parents (such as Disobedience, or Mind What Mama Says, and Happy Because Good). She married Thomas Traill, a retired officer of the Napoleonic Wars and a friend of her sister's husband John Moodie, although the rest of her family (aside from Susanna) did not approve of him. Soon after their marriage they left for Canada, with Susanna's family, settling near Peterborough, Upper Canada, where her brother Samuel was a surveyor.
She described her new life in letters and journals, and collected these into a book in 1836, The Backwoods of Canada, which is an important source of information about early Canada. She describes everyday life in the community, the relationship between Canadians, Americans, and natives, as well as the climate and wildlife. More observations were published in Canadian Crusoes in 1851. She also collected information concerning the skills necessary for a new settler, published in two books, one in 1854 as The Female Emigrant's Guide and the second in 1855 as The Canadian Settler's Guide.
After suffering through the depression of 1836, her husband Thomas joined the militia in 1837 to fight against the Upper Canada Rebellion. In 1840, dissatisfied with life in "the backwoods," the Traills and the Moodies both moved to the city of Belleville. While Susanna was more concerned with the differences between rural and urban life, Catharine spent her years in Belleville writing about the natural environment. She often sketched the plant life of Upper Canada, publishing Canadian Plant Life in 1865 and Studies of Plant Life in Canada in 1885.
She died in 1899. Catharine Parr Traill College, a campus of Trent University in Peterborough, is named for her.