He matriculated with s Bachelor of Scientific Agriculture from the University of British Columbia, Canada in 1935. He worked for Golf course architect Thompson-Jones & Company, Toronto, Canada, from 1935 to 1947 with the exception of time spent in the military.
He served with the Canadian Armed forces in WWII achieving the rank of Major.
Lewis immigrated to the United States in 1947. he served as an instructor at the University Massachusetts from 1947-1952 while simultaneously working on his Masters. In 1952 he earned his Master of Science from the University of Massachusetts. He became a naturalized U.S. citizen in 1955.
After obtaining his Masters degree in 1952, Geoffrey Cornish established a private practice as a golf course architecture headquartered in Amherst, Massachusetts.