Associate Architect, Bellante and Clauss, London, UK, 1951-1958; Partner, Mitchell / Giurgola, Architects, Philadelphia, PA, 1958-1984, and New York, NY, 1966-1984; retired in 1984; Partner, Mitchell / Giurgola and Thorp, Architects, Canberra, Australia, 1980-1984;

Visiting Lecturer, Dartmouth College; Boston Architectural Center; California State Polytechnic University, San Luis Obispo; Neocon, Chicago, IL; University of Kentucky, University of Maryland, University of Washington, Saint Louis, MO; University of Arizona; University of Brasilia, Brazil; the Ohio State University, Columbus, OH; University of Utah; University of Nebraska; University of Texas, Dallas;

Mitchell was a Registered Architect in the States of PA (1951), as well as NY, NJ, DE, MA, IN, CT, WA, IL, FL, VA, MO, NC, SC, DC and the Australian Capital Territory c. 1985; Member, Board of Directors, American Institute of Architects, Philadelphia Chapter, 1964-1968; Member, Board of Directors, Pennsylvania Society of Architects, 1964-1965; Secretary, Pennsylvania Society of Architects, 1966; Vice-President, Pennsylvania Society of Architects, 1967; President, Pennsylvania Society of Architects, 1968; President's Council, American Institute of Management, 1967; President, Member, Board of Directors, American Institute of Architects, 1973-1979; Vice-President, American Institute of Architects, 1976-1977; First Vice-President, American Institute of Architects, 1978; President, American Institute of Architects, 1979; in c. 1985, Mitchell was NCARB certified; Member, Philadelphia Contruction Industry Council; Member, Architectural League of New York;

Fellow, American Institute of Architects, 1969; Honorary Fellow, Royal Canadian Institute of Architects, 1979; Fellow, Royal Australian Institute of Architects, 1980; Honorary Member, Sociedad Arquitectos Mexicanos, 1980;

A.B. (1947), B.Arch. (1948), University of Pennsylvania, Philadelphia, PA, 1941-1944, 1946-1948;

Emerson Architectural Prize, University of Pennsylvania, Philadelphia, PA, 1948; Faulty Medal in Architecture, University of Pennsylvania, Philadelphia, PA, 1948;

Mitchell suffered from multiple sclerosis for the last twenty years of his life.