The first wife of oceanographer William Beebe, Niles also wrote under the name of Mary Blair Beebe. She lived among indigenous peoples in Mexico, South America, and Southeast Asia. In 1923 she published Casual Wanderings in Ecuador. Colombia: Land of Miracles followed in 1924, and Peruvian Pageant in 1937. In these books she linked contemporary culture with the past by exploring history, traditions, and legends. She visited the notorious Devil's Island in 1926 and recorded the life of a prisoner there in her 1928 best selling biography: Condemned to Devil's Island. The international sensation caused by this book led to prison reforms. Her 1931 book, Strange Brother, is an account of homosexuality in New York City during the Harlem Renaissance and her only book gay-themed work. In 1944 Blair Niles was awarded the Gold medal of the Society of Woman Geographers.

Non-Fiction

• Casual Wanderings in Ecuador (1923)
• Colombia: Land Of Miracles (1924)
• Black Haiti: A Biography of Africa's Eldest Daughter(1926)
• Strange Brother (1931)
• Peruvian Pageant, A Journey In Time (1937)
• The James: From Iron Gate to the Sea (1939) (Rivers of America Series)
• Passengers to Mexico: The Last Invasion of the America's (1943)
• Martha's Husband: An Informal Portrait of George Washington (1951)

Fiction

• Condemned to Devil's Island (1928) - turned into the 1929 film Condemned
• Free (1930)
• Maria Paluna (1934)
• Day of the Immense Sun (1936)
• East by Day (1941)