Marshall and the Attorney General persuaded President Kennedy to enforce the order using federal troops.
Within two years of coming into office, he had launched 42 federal lawsuits against states to reform their electoral legislation.
He argued to not use the Fourteenth Amendment to overcome discrimination, instead favoring the federal government's constitutional power to regulate interstate commerce.
Marshall used it as a basis to write the 1964 Civil Rights Act, which prohibited discrimination in public facilities, in government and in employment.
Marshall's reputation was not that of an office-based bureaucrat, but of a hands-on negotiator who dealt with many of the major figures across the civil rights drama, ranging from Martin Luther King Jr. to Alabama Governor George Wallace.
President Lyndon B. Johnson wrote on Marshall's formal letter of resignation, "I have never known any person who rendered a better quality of public service."
After leaving government, Marshall returned to commercial legal practice, briefly rejoining Covington and Burling before becoming a vice president and general counsel at IBM in 1965.
Marshall died June 2, 2003, aged 80, at his home in Newtown, Connecticut, of complications of myelodysplasia, a bone marrow disorder.