Marston was chosen to be the dean of the University of Mississippi's School of Medicine and director of the university's Medical Center in Jackson, Mississippi in the midst of the Civil Rights Movement in 1961. Marston was hired with the tacit understanding that he would integrate the medical school and medical center to comply with Federal law and maintain the medical school's accreditation. Under his politically understated guidance, and in the face of continued political opposition from Mississippi Governor Ross Barnett, his administration admitted the first African-American medical students, hired the first black medical professor, integrated the medical center's patients, and set new precedents for the non-violent racial desegregation of Southern medical schools and teaching hospitals. Later, in 1965, he was chosen to be the university's vice-chancellor.