Donald Insall studied at the RWA School of Architecture (since Bristol University), the Royal Academy and the School of Planning in London and was Letharby Scholar of the Society for the Protection of Ancient Buildings. He founded his own architectural and planning consultancy in 1956 named Donald W. Insall & Associates whose practice has included town-centre studies, civic sites, university, domestic and other buildings, notably in conservation of historic towns and buildings including the restoration of the ceiling of the House of Lords, and Windsor Castle. His consultancy's recent projects have included the refurbishment of the Courtyard at Somerset House, completed in the Spring of 2000 and the refurbishment of the Royal Holloway College Founder's Building described by Pevsner as 'the most ebullient Victorian building in the Home Counties'.
Donald Insall has also held Visiting Lectureship posts at the Royal College of Art, between 1964 and 1969, at the International Centre for Conservation in Rome, the College d'Europe in Bruges and has been the Visiting Professor to the Catholic University of Leuven from since 1977. He has won several awards including the Queen's Silver Jubilee Medal in 1977, the European Prize for Preservation of Historic Monuments in 1981 and the Europa Nostra Medals of Honour in 1983 and 1989 amongst others. His practice has received over one hundred International, National, Architectural and Craftsmanship Awards.
He received the OBE in 1981 and the CBE in 1995. He is a Fellow of the Society of Antiquaries of London, a Fellow of the Royal Institute of British Architects and a Fellow of the Royal Town Planning Institute.