Dr. Earle was born in Leicester, Massachusetts. He received his education at the local Academy and Friends School in Providence, Rhode Island, and graduated in medicine in 1837 from the University of Pennsylvania. In 1840, he was a resident physician at the Friends Hospital in Frankford, Pa., and in 1844, he was appointed Medical Superintendent at Bloomingdale Asylum in New York City, where he remained for five years before embarking on a second trip to Europe to visit asylums. On his return to New York City, he was appointed a visiting physician to the New York Asylum and served as a lecturer on mental diseases at the College of Physicians and Surgeons.
In 1864, Dr. Earle became superintendent of the Northampton Lunatic Hospital in Massachusetts, where he remained for 22 years until his retirement. Dr. Earle was a prolific writer with a special interest in hospital statistics. In 1822, he published “The Curability of Insanity,” which questioned the existing statistics for cures for mental illness. He wrote the chapter on “Insanity” for the U.S. Census in 1860. He was an organizer of the American Medical Association and the New York Academy of Medicine. He was an honorary member of the Medico-Psychological Association of Great Britain for 48 years. Dr. Earle was one of the founders of the Association of Medical Superintendents of American Institutions for the Insane and served as President (1884–1885).