 Williams began his career as a researcher as an assistant professor of astronomy at the University of Michigan, and from 1945, associate professor of physics.A growing fascination with viruses led him to leave Michigan in 1950, when he was invited to the University of California, Berkeley by Wendell Stanley, to serve as a professor at the newly created Department of Virology.Together with Heinz Fraenkel-Conrat, Williams studied the Tobacco mosaic virus, and showed that a functional virus could be created out of purified RNA and a protein coat.