The agency has been appointed to offer strategic PR advice and handle media enquiries surrounding her involvement in the bid.
A source close to the hire says Cassani saw three agencies before selecting Brunswick, with which she has worked in the past.
The agency handled the sale of Go, the airline she led during and after its time as a British Airways subsidiary. BA is also a client of Brunswick.
The Brunswick team working for Cassani includes former BA head of communications, now partner, Nick Claydon, Mike Smith, who is also a partner and senior associate partner Ed Williams.
A source stressed Brunswick is not handling PR for the bid itself. The recruitment of external support for this will be made once Cassani appoints a senior in-house PRO. The source added that Cassani aims to be heavily involved in the selection of external support.
Cassani was appointed last week as chair of the bid committee in an appointment made by the three partners involved – the British Olympic Association. the Department of Culture, Media and Sport and the Greater London Authority.
The Brunswick hire comes two weeks after the appointment of Capital PR to handle interim comms surrounding the bid. That work is handled by Capital director Jackie Brock-Doyle (PRWeek, 13 June).