After earning his MBA in 1968, he joined Bell and Howell Communications Company as vice president of the education group. He left to cofound Keller Graduate School of Management in 1973. In 1987, Keller Graduate School acquired the assets of DeVry, Inc., the holding company for the DeVry Institutes of Technology.

Keller has been a director of Templeton, Kenly & Co., Precision Plastics of Indiana, Inc., NICOR, Inc., the Chicagoland Chamber of Commerce, and the Great Books Foundation; chairman of the Council on Chicago Booth and Princeton University's School of Engineering and Applied Sciences Leadership Council; vice chairman and trustee of the Chicago Zoological Society; and trustee of the Glenwood School for Boys, the George M. Pullman Education Foundation, and Princeton University. In April of 1996, Keller was appointed to the Illinois Human Resource Investment Council by Governor Jim Edgar.