Born in London England, to a wealthy family with ties to royalty, she became a noted long-time resident artist of Taos, New Mexico. She grew up in the court of Queen Victoria and took dancing lessons with the Queen's grandchildren. Dorothy saw her first American Indian at the age of five, attending a performance of Buffalo Bill's Wild West Show. She was determined to become an artist, which was not at all part of her parent's expectations of her socially. Dorothy enrolled in the Slade School of Art in 1910, and graduated six years later. Titled the "Honorable Dorothy Brett", she also attended University College.

She began painting portraits of English celebrities including novelist D.H. Lawrence, she went to Taos with him and his wife in 1924. Dorothy then became a U.S. citizen in 1938. She began painting Indian genre but was hesitant because of her landscape and portrait background, her first Indian depiction was of a rabbit hunt. She became a close friend of artist and socialite Mabel Dodge Luhan. Dorothy, Luhan and Frieda Lawrence became fixtures of society in Taos and were known as the Three Fates. They were marked by their attachment to D.H. Lawrence.

Brett is one of the earliest established Taos artists. Her painting style is primitive, and her expressions of Indian life romanticized.