Prior to forming his own firm, Klein worked as an architect for the New York office of I.M. Pei and Partners. At Pei, he helped to design the Augusta Civic Center and the Indiana University Museum of Fine Arts. He also worked for James S. Polshek and Partners, where his design for the Rochester Convention Center won a First Award from Progressive Architecture. While working as a project manager for William M. Bodouva and Associates, he contributed to plans for the Garden State Plaza mall, Bloomingdale’s, J. C. Penney, Newark Airport, Stewart Airport, the Port Authority Bus Terminal, and Journal Square Plaza. In addition, Klein has taught architecture at Yale University.