Simpson studied architecture at University College London.

Simpson is Principal of John Simpson Architects LLP, Chartered Architects and Urban Designers, London.

He is a member of Royal Institute of British Architects. Simpson is part of the New Classical Architecture movement of contemporary architects designing in classical styles. A profile of Simpson's design for his own house featured on the Sky Arts programme The Art of Architecture in 2019.^[1]

In 1991, Simpson architected Ashfold House in West Sussex.

• Masterplan for the area around St Paul's Cathedral, London (1992–1996).
• The West Range of Gonville Court, Gonville and Caius College, Cambridge (1993–1996)^[2]
• New buildings for Lady Margaret Hall, Oxford (2010–2017).
• The Queen's Gallery, Buckingham Palace, London (2002).
• Masterplan for Fairford Leys, a village outside Aylesbury, Buckinghamshire.
• Walsh Family Hall of Architecture, University of Notre Dame (2019)
• Masterplan to reorganize Kensington Palace into a public visitor and community facility (2008–2012).

• Richard John and David Watkin, John Simpson; The Queen's Gallery, Buckingham Palace and Other Works. Andreas Papadakis pub, London, 2002.
• David Watkin, The Architecture of John Simpson: The Timeless Language of Classicism. Rizzoli International Publications, 2016.

• John Simpson Architects LLP