Dean is the son of Joseph Dean, a judge, and grew up in Wye in Kent, one of the English Home Counties. One of his sisters is Tacita Dean, the artist.

He studied architecture first at the Bartlett School of Architecture at University College London, then continued with a post-graduate diploma in architecture from Edinburgh University. At Edinburgh, Dean studied under late-modernist Professor Isi Metzstein.

Architecture

After finishing his academic studies, Dean received funding from the International Council on Monuments and Sites (ICOMOS) to document mud adobe structures in New Mexico and Arizona. He then worked for Peter Inskip and Peter Jenkins Architects on a variety of Grade I listed buildings, including Stowe House, Chastleton House and Waddesdon Manor.

Ptolemy completed the Society for the Protection of Ancient Buildings Scholarship.

He has worked for a number of Britain's more traditionally influenced architects, including Sir William Whitfield, neo-classicist John Simpson, Sir Frederick Gibberd and Richard Griffiths. At Richard Griffith's, he provided heritage assistance in obtaining planning consent for RHWL architects' post-modern influenced extension to St Pancras Chambers.

He now runs his own small practice, Ptolemy Dean Architects, near Borough Market in London.

Books

Dean has written and illustrated two books on the 19th century British architect Sir John Soane, and co-written a study of London's Borough Market.

Television

Dean has appeared with Marianne Suhr as the resident "ruin detective" on the BBC Two television programme Restoration. In his seven-episode series The Perfect Village, on BBC Four, Dean visited 12 English villages and discussed the qualities that would create the "perfect village."

Art and illustration

As seen in his television appearances, Dean produces watercolor cityscapes and architectural renderings or illustrations. These are done in a wobbly line pen and ink technique with evocative color washes, and are vaguely close to the style, technique, and subject matter of the architect and artist Sir Hugh Casson.