Gustafson graduated summa cum laude from Bob Jones University in 1978, and with distinction from the Duke University School of Law in 1981, where he was a member of the Order of the Coif and executive editor of the Duke Law Journal (1980–1981). Gustafson was admitted to the District of Columbia Bar in 1981 and served as an associate at the law firm of Sutherland, Asbill and Brennan, in Washington, D.C., 1981-1983. He was a trial attorney (1983–1989), Assistant Chief (1989–2005), and Chief (2005–2008) in the Court of Federal Claims Section of the Tax Division in the U.S. Department of Justice; and Coordinator of Tax Shelter Litigation for the entire Tax Division (2002–2006). He won Tax Division Outstanding Attorney Awards in 1985, 1989, 1997, 2001–2005, and the Federal Bar Association's Younger Attorney Award, 1991. He was elected president of the Court of Federal Claims Bar Association (2001) and was appointed by President George W. Bush as Judge, United States Tax Court, on July 29, 2008, for a term ending July 29, 2023.
Gustafson married Sharon Elizabeth Fast in 1980 and they have nine children. Gustafson's father was the late composer Dwight Gustafson.