A Tennessee native, Marston graduated with a B.A. from Maryville College and in 1967 with a J.D. from Harvard Law School in Cambridge, Massachusetts.
In a 2007 interview with John Gizzi of the conservative publication Human Events, Marston recalled that President Carter had vowed if elected to "appoint and retain attorneys solely on merit," a reform commitment in the post-Watergate climate which was even written into the platform of the 1976 Democratic National Convention.