Dr. Preston was born in Washington County, Virginia. He attended Abingdon Academy and Emory and Henry College in Virginia, and then studied medicine at the University of Virginia, graduating in 1867. He served his state during the Civil War as a captain in the 21st Virginia Calvary.
In 1887, he became an assistant physician at the Southwestern State Hospital for the Insane, and in 1888, he was promoted to Superintendent, a post he held until his death.
Dr. Preston was President of the Virginia Medical Society in 1894 after being a member for 23 years, and he was awarded an honorary fellowship in 1895. In addition, he received honorary fellowships from the Lynchburg, Va., Academy of Medicine and the Boston Gynecological Association. He made numerous contributions to the medical literature. Dr. Preston was President of the American Medico-Psychological Association (1901–1902).