After completing his graduate studies, Berg spent two years (1952–1954) as a postdoctoral fellow with the American Cancer Society, working at the Institute of Cytophysiology in Copenhagen, Denmark and the Washington University School of Medicine, and spent additional time in 1954 as a Scholar in Cancer Research with the Department of Microbiology at the Washington University School of Medicine. He worked with Arthur Kornberg, while at Washington University. Berg was also tenured as a research fellow at Clare Hall, Cambridge. He was a professor at Washington University School of Medicine from 1955 until 1959. After 1959, Berg moved to Stanford University, where he taught biochemistry from 1959 until 2000 and served as Director of the Beckman Center for Molecular and Genetic Medicine from 1985 until 2000. In 2000 he retired from his administrative and teaching posts, continuing to be active in research.