Willis began his private practice in 1993 following a six year association with Robert Venturi and Denise Scott-Brown where he was a project architect and involved with several internationally recognized projects: the Sainsbury Wing to the National Gallery of Art in London, England, Fan Pier High Rise Apartments in Boston, Massachusetts, Laguna Gloria Art Museum in Austin, Texas, the Philadelphia Philharmonic Hall, the Seattle Art Museum and private residential projects throughout the United States. He graduated Magna Cum Laude from Brown University as an undergraduate and pursued a two year graduate program of Fine Arts at the University of Wisconsin, and received a Masters of Architecture from the University of Pennsylvania in 1985.