Mary O'Hara Alsop was born in Cape May Point NJ, the third child of a Reverend and his wife. She was raised in Brooklyn Heights, New York. In 1905 she married her third cousin, Kent Kane Parrot, with whom she had two children, the first of which died of skin cancer in her early teens.
She divorced Parrot and went to work as a Hollywood screenwriter in the 1920s. In In 1922 she married Helge Sture-Vasa and moved with him to Wyoming. In 1930 they bought a ranch, which they renamed Remount Ranch, and stocked it with sheep. The Great Depression ended the profitability of sheep and the couple managed to get by by delivering milk in Cheyenne and breeding horses, and on O'Hara's writing income. She wrote mainly Wyoming ranch stories, and is best known for My Friend Flicka (1941), Thunderhead (1943), and Green Grass of Wyoming (1946).
In 1946 O'Hara and her husband sold the ranch and purchased one in California. The following year they divorced, and O'Hara moved to Monroe CT where she continued to write. In 1968 she moved to Chevy Chase MD, where she lived until she died of arteriosclerosis.
