In 1953 Spong was elected as ato the House of Delegates, where he served one term. During that time he was identified as one of the “Young Turks” who were challenging the leadership and policies of the , the Democratic political machine run by In 1956 Spong was elected to the Senate of Virginia, where he served for a decade. He opposed legislation, voting instead for the local option plan, which permitted some integration of public schools. From 1958 to 1962, Spong was the chairman of the Commission on Public Education, which produced a noteworthy study of the needs of Virginia public schools during his tenure.
In 1966 Spong ran againstfor a seat in the United States Senate. This proved to be a pivotal race that ended the Byrd regime’s long control of Virginia politics. In an indirect attack on Robertson’s age and the Byrd Organization’s inertia, Spong characterized himself as “A Man for Today,” rejecting the status quo and calling for forward-looking leadership. He criticized Robertson’s votes against education, water pollution, and urban mass transit legislation as unresponsive to the needs of a changing Virginia. He won the hotly contested race by a meager 611 votes.
In the Senate, Spong served on the Public Works and Foreign Relations committees and helped to write the Clean Air Act and the War Powers Act. He also won attention for his controversial vote against President Richard Nixon’s nomination of G. Harrold Carswell to the United States Supreme Court, which was rejected by the Senate. A moderate, soft-spoken individual known for his integrity and good humor, Spong once told an audience at the National Press Club that he and senators Russell Long and Hiram Fong were going to introduce a bill to protect the rights of songwriters in Hong Kong. The legislation, he joked, would be known as the Long Fong Spong Hong Kong Song Bill.
Spong was defeated for reelection in 1972 by Representative William Scott, who waged an aggressive media campaign against him, tying him to the anti–Vietnam War record and liberal social agenda of Democratic presidential candidate George McGovern. Spong did not respond to these attacks and went down to defeat in the Nixon landslide against McGovern.
In retirement Spong returned to the practice and teaching of law. From 1976 to 1985 he served as professor of law and dean of the Marshall-Wythe School of Law at the College of William and Mary. He is credited with improving the law school’s reputation by upgrading its facilities and increasing the size of the student body and faculty. He served as president of the Virginia Bar Association in 1976 and was the court-appointed mediator in numerous legal cases—notably, the Westinghouse uranium case and the punitive damages litigation in the suits against the A. H. Robins Company, manufacturer of the faulty Dalkon Shield contraceptive device. Spong also continued his public service with terms on the State Council of Higher Education, the Board of Visitors of William and Mary, and other philanthropic boards. He served as interim president of Old Dominion University from 1988 to 1990.
Spong married Virginia Galliford in 1950; they had one son and one daughter. He died in Portsmouth on October 8, 1997, and is buried at the University of Virginia cemetery in Charlottesville.