Ken Prewitt was born in 1936 in Alton, IL. He attained his B.A. from Southern Methodist University in 1958 before earning his M.A. the next year from Washington University; he also attended the Harvard School of Divinity. In 1963, he earned his Ph.D. in political science from Stanford University.

From 1965 until 1983, Prewitt taught at the University of Chicago, eventually achieving the rank of full professor. Additionally, he taught at Stanford, Columbia, Washington and Makerere Universities. Prewitt was also senior vice president of the Rockefeller Foundation for ten years, and served for five years as director of the National Opinion Research Center.

President Bill Clinton appointed Prewitt to replace the departing Martha Farnsworth Riche as director of the Census Bureau in 1998. From this post, he led 2000 census efforts, including the Census Bureau's planned but not enacted sampling proposal. Since his resignation in 2001, Prewitt has published many books and articles, including several about the census and was a professor and fellow at the School of International and Public Affairs at Columbia University.

In April 2021, Dr. Prewitt returned to the Census Bureau as a senior advisor in the Office of the Director.