In 1980, Williams joined the faculty of George Mason University in Fairfax, Virginia, and is currently the John M. Olin Distinguished Professor of Economics. He has also served on the faculties of Los Angeles City College (1967–69), California State University (1967–1971), and Temple University (1973–1980). From 1963 to 1967, he was a group supervisor of juvenile delinquents for the Los Angeles County Probation Department.

More than 50 of his publications have appeared in scholarly journals such as Economic Inquiry, American Economic Review, and Social Science Quarterly as well as in popular publications such as Reader's Digest, the Wall Street Journal and Newsweek. He has made many TV and radio appearances on such programs as Milton Friedman's Free to Choose, William F. Buckley's Firing Line, Face the Nation, Nightline, and Crossfire. He is also the author of Race and Economics: How Much Can Be Blamed on Discrimination? and Up from the Projects: An Autobiography.

Williams sits on many advisory boards, including the Review Board of Economics Studies for the National Science Foundation, the Research Foundation, the National Tax Limitation Committee, the Taxpayer's Foundation, and the Hoover Institution.

Williams holds a bachelor's degree in economics from California State University, and a master's degree and doctorate in economics from the University of California–Los Angeles.