Peter Clark was raised in Illinois, where he graduated from New Trier Township High School. He was in the United States Army from 1965 to 1968, including Vietnam service with the 1st Infantry Division. He is a graduate of the University of Illinois and Yale Law School and a member of the Massachusetts Bar. He has been a county prosecutor, counsel to state mental health and social service agencies, a legal aid lawyer, and an Assistant Attorney General in Massachusetts. He currently serves in the U.S. Department of Health & Human Services in the Office of the Inspector General.