Stewart spent most of his career as a professor of Agricultural Engineering at Iowa State University. He received all of his degrees, including his Ph.D. from Iowa State. He worked for 34 years as an extension agricultural engineer in Iowa working as a soil, water and waste management specialist prior to retiring from ISU in 2004. His first engineering job was with the Soil Conservation Service in East Central Iowa. He has academic experience at Colorado State University and at Silsoe College in Bedfordshire, UK. He was Head of the Agricultural and Biosystems Engineering Department at ISU for eight years.
Upon retirement from ISU, he joined CWA to work on animal waste management issues, as well as other soil and water engineering projects. He has had international consulting experience in Europe, South America, SE Asia, and Mexico. He has been a licensed engineer in Iowa since 1969.