Among Harrison's most noted projects are the Metropolitan Opera House at the Lincoln Center for the Performing Arts and the Empire State Plaza in Albany; he also served as Director of Planning on the United Nations complex, which was built on slaughter-house property contributed by the Rockefeller family (the Rockefellers owned the Tudor City Apartments across First Avenue). Harrision also developed the design for the Pershing Memorial in Washington, D.C. (today referred to as "Pershing Park", and home to the National World War I Memorial. In addition to his architectural work, Harrison served as master planner and supervising architect for a number of important Long Island-based projects, including the World's Fairs of 1939 and 1964 in Flushing, Queens, and LaGuardia and Idlewild (now John F. Kennedy) airports.