He and former classmate George Haller established a partnership in 1962, and grew it into the successful firm H&L is today. Larson was the project architect on several major buildings for CU-Boulder, including the present-day Engineering Center, the Biosciences Building, and additions to Muenzinger Psychology and the Coors Events Center. His other projects include several school buildings for the Cherry Creek School District; Silver Creek High School in Longmont; and hospital buildings for Presbyterian-St. Luke's, Swedish Medical Center, and Craig Hospital. He is a fellow of the American Institute of Architects and has served as president of both the Colorado and Denver chapters of AIA, in addition to teaching at the University of Colorado Denver's College of Architecture and Planning.