She takes over the running of the annual event from fair director Gillian Craig, who will step down in September after 23 years.
Williams, formerly an events manager at Guardian News and Media and, before that, at the Victoria & Albert Museum, will take up the role in August. The next BADA fair runs from March 9-15, 2016, at Duke of York Square in London's Chelsea.
Craig announced her decision to step down immediately after the close of the 2015 fair. She has organised the event from its inception in 1993, after being approached by the BADA following her organisation of The Burlington House Fair at the Royal Academy. "My task was to start the BADA fair and to establish it in the international calendar of leading art and antiques fairs. Now, Madeleine will evolve it and carry it forward," said Craig.
Richard Coles, BADA fair chairman, says that Williams' "organisational skills and experience in multi-platform marketing will bring great energy to the event". Craig will remain in a consultancy role for six months as a hand over.