Bernard Melchior Feilden was born in Hampstead, North London on 11 September 1919, a twin and one of five sons of Humphrey and Olive Feilden. His grandfather had been Ipswich architect Brightwen Binyon (1846-1905), a former pupil of Alfred Waterhouse. The family soon emigrated to Canada, in the hope of an improvement of his father's health after he was gassed during the First World War. Nine years later, his father was drowned in a lake there - a tragedy witnessed by the boy. The family then returned to England and the children were raised by their mother and aunts in Bedford.
The young Feilden attended Bedford School, the Bartlett School of Architecture at University College London, and the Architectural Association.
During the Second World War, he served in the Bengal Sappers and Miners in India, Meopotamia, Iran and Italy. On his return from war service, he completed his architectural training at the Architectural Association. He then secured a post in the Norwich practice of Edward Boardman & Son, where he designed the Trinity United Reformed church. In 1949 he married Ruth Bainbridge, with whom he would have two sons and two daughters.
He commenced independent practice in Norwich in 1954, in partnership with David Mawson under the title Feilden & Mawson. The practice later opened offices in London, Cambridge and Prague. Feilden was appointed consultant architect to the University of East Anglia, and was responsible for the design of many of the campus buildings. He was elected FRIBA on 6 October 1965, his proposers being Donovan Purcell, David Eyre Percival and Edward Ray Crane.
By that time Feilden had come to specialise in conservation architecture; and the loss of his left eye in a shooting accident did nothing to hold him back from becoming a key figure in his field, though he always advocated turning to conservation only in the middle of one's career: 'Become a good architect first, and then become a good conservation architect.' In 1962 he had saved the spire of Norwich Cathedral from demolition after wartime air-raid damage, by devising a strengthening scheme for the structure in collaboration with Bertrand Monnet of Chartres and Strasbourg. He had also inserted new foundations under the tower of York Minster to stop it from sinking. His notable role in conservation continued with his 1969 appointment as Surveyor of St Paul's Cathedral, and he was instrumental in gathering funds and support for the repairs and alterations that had been made necessary by the damage that this building, too, had suffered during wartime bombings.
On resigning his St Paul's Surveyorship in 1977, he was appointed director of the International Centre for the Study of the Preservation and Restoration of Cultural Property (ICCROM) in Rome, advising on worldwide projects such as the al-Aqsa Mosque in Jerusalem, his plans for the dome of which won him the Aga Khan Award in 1986. He carried out several UNESCO missions, advising on the structural condition of the Taj Mahal and of the Sun Temple at Konarak in Orissa. He was also widely consulted on China's architectural and cultural heritage including Beijing's Forbidden City, the Great Wall, the Mogao Caves, the Terracotta Soldiers in Xian, and the buildings of Mount Taishan. Back in Britain, in 1975 he led the movement to safeguard the historic centre of Chesterfield in Derbyshire, for which he received a 1982 Europa Nostra Silver Medal; in the early 1980s he worked in collaboration with Simpson & Brown on the restoration of St Giles' Cathedral, Edinburgh; and he advised on the restoration of Marlborough House in Pall Mall and of Hampton Court Palace. He was consulted on the conservation of the Parliament Buildings in Wellington, New Zealand.
Feilden was a representative of the RIBA on the Ancient Monuments Board from 1962 to 1977, was a member of the RIBA Council from 1976 to 1977, and was president of the Ecclesiastical Architects' Association and of the Guild of Surveyors in 1976, and of the International Council on Monuments and Sites from 1981 to 1987. He had a deep religious affinity with ecclesiastical buildings, and was a member of the Cathedrals Advisory Commission for England from 1981 to 1991. He lectured widely in India and in the United States - at the universities of Berkeley, Columbia, Columbus, Cornell, Pennsylvania and Virginia - where he was an honorary Fellow of the American Institute of Architects. He also wrote a number of important books on architectural conservation: 'The Conservation of Historic Buildings' (1982); 'An Introduction to Conservation' (UNESCO, 1980); 'A Manual for the Management of World Cultural Heritage Sites (UNESCO, 1993); 'Between Two Earthquakes' (UNESCO, 1987); and 'Guidelines for Conservation in India' (UNESCO, 1989). He was recognised by honorary doctorates from the universities of York, Gothenburg and East Anglia, and a Fellowship at University College London, and was appointed OBE in 1969, CBE in 1976 and a knight of the realm in 1985.
Feilden's first wife, Ruth, died in 1994; he subsequently remarried. Feilden died on 14 November 2008, survived by his second wife, Tina, and his four children.