Baker earned a Ph.D. degree from the University of Illinois at Urbana-Champaign in 1965; his thesis was titled Qualitative and Quantitative Evaluation of the Amino Acid Needs of Adult Swine for Maintenance.[6] He then spent two years as a senior scientist with the Eli Lilly and Company in Indianapolis, Indiana, then returned to join the University of Illinois at Urbana-Champaign faculty in the Department of Animal Sciences and Division of Nutritional Sciences, where he remained for the rest of his career.
Baker published 510 peer-reviewed papers, mainly in non-ruminant nutrition (i.e., swine and poultry nutrition), with research and teaching emphases on nutritional principles involving amino acids, minerals, vitamins, and other nutrients.