Dr. Barrett was born in Austin, Illinois, educated in Iowa City, and received his B.A. (1893) and M.D. (1895) from the State University. His first position was as a psychologist at the State Hospital for the Insane in Independence, Iowa (1895–1997), followed by a year as a physician at Worcester State Hospital in Massachusetts. He returned to Independence (1898–1901) and then spent a year in Germany studying at Heidelberg. He returned to Massachusetts and took a position as a pathologist at Danvers State Hospital. He was also an assistant neuropathologist at Harvard University (1905–2006).
In 1906, Dr. Barrett became the first director of the new psychopathic hospital located in Ann Harbor, Michigan, and the first research institution to be associated with a university. He was also a professor of psychology and nervous diseases and, after 1920, chairman of the Department of Psychiatry. This institution became a model for psychiatric hospitals in Massachusetts, New York, and elsewhere.
Dr. Barrett contributed to psychiatric literature. He supported a dynamic approach to problems of mental health, but his interest in neuropathology continued. He was an authority on the relationship of arteriosclerosis and pernicious anemia to mental disease. He was nominated for the Salmon Lectureship (1937) before he died.
He was active in medical societies, including the National Committee for Mental Hygiene, the American Psychological Association (President, 1985), and the American Neurological Association (President, 1925–26).
Dr. Barrett was President of the American Medico-Psychological Association (1921–22).