Doris Shannon Garst was born on July 24, 1899, in Ironwood, Michigan, to Julius Jensen and Zenta Shannon Jensen. When she was four years old, her family moved west to Denver, Colorado. She attended Denver's public schools until her senior year of high school, when her family moved to Hood River, Oregon, where they had purchased a fruit orchard. After teaching for four years at an Oregon country school, she moved to Wyoming to accept a civil service job. In Wyoming she married Joseph Garst, an attorney whose family once owned the building that eventually became the county museum that housed the Annie Oakley memorabilia. The couple had three children. Garst co-authored three books with her son Warren: Wild Bill Hickok, Cowboys and Cattle Trails, and Ernest Thompson Seton: Naturalist.
Concerning her prolific writing career, Garst says that she was born with the urge to write and often wrote stories during her childhood. She wrote her later stories to entertain her own children. Busy with her responsibilities as a wife and mother, Garst admits that she may not have had any time to write if her daughter Barbara had not contracted scarlet fever. Victims of scarlet fever were quarantined in those days, and Garst wrote her first book while staying home with her daughter.
Steeped in the lore of the American West throughout her childhood, she naturally became interested in the region's legendary, but real, people. Her biographical novels about heroes result from her own desire for adventures, and she says that historical events provide much more exciting stories than the fiction dreamed up by writers of western fiction or the producers of western movies.
She has received numerous awards, including the Young Reader's Choice Award of the Pacific Northwest Library Association and the Boys' Club of America Junior Book Award, both for Cowboy Boots. She also received awards in 1953, 1954, 1955, and 1957 from the National Federation of Press Women; Red Eagle was chosen as a Junior Literary Guild selection in 1959; and she won the Wyoming State Historical Award for Broken-Hand Fitzpatrick in 1961.