Mary Blair Rice, better known by the pen name Blair Niles, was born at The Oaks, her parent's tobacco plantation that lay along the muddy banks of the Staunton River in Coles Ferry, Virginia. She was the daughter of Henry Crenshaw and Marie Gordon Peyor Rice. Both her parents came from families with long ties to Virginia. As a child she would spend hours alone in the family library reading about the outside world or quizzing the mostly black servant staff about life beyond the plantation's tobacco fields.
On 6 August, 1902 Blair married William Beebe, a well known naturalist and explorer, who at the time was head curator of the New York Zoological Gardens in Bronx Park. Over the next decade the couple would travel the world exploring some its more remote regions. During these forays she worked as his assistant and would later help him write several books about their travels. She also wrote under the name of Mary Blair Beebe.
In 1913 she married architect Robert Niles after divorcing Beebe earlier in the year. William shared Blair's passion to explore faraway and exotic lands and would accompany her on many expeditions throughout South and Central America where he would gain some notoriety for his photography.
It was while in French Guiana that Blair gathered material that became the genesis for her 1927 book Condemned to Devil's Island and the film Condemned! (1929). She is thought to have been the first woman to do research on the infamous French penal colony which she called "the dry guillotine". The international sensation caused by this book led to prison reforms.
Her 1931 book, Strange Brother , was a gay-themed novel (her only work in that genre) set in New York City during the Harlem Renaissance. The story is about a platonic relationship between a heterosexual woman and a gay man. She was a popular novelist who, though heterosexual, wrote sympathetically about gay life.
Besides her travels, Blair Niles also wrote about Maximilian and Carlota "Passengers to Mexico" (1943), "George Washington", "Martha's Husband" (1951) and a volume in the "Rivers of America" series entitled "James: From Iron Gate to Sea" (1945). The city of Lima, Peru gave her a gold medal for her 1937 travel book, "Peruvian Pageant" and in 1944 she was awarded a gold medal from the Society of Women Geographers.
Blair Niles died from a cerebral hemorrhage in New York City.