Bonnay was elected 23 March 1789, by the Second estate of the bailiwick of the Nivernais and Donziois as a substitute deputy to the Estates General; he was admitted to sit 21 July in replacement of the comte de Damas d'Anlezy, who resigned.
On the Flight to Varennes (20-21 June 1791), Bonnay was accused of having inside knowledge of the event prior to the royal family's departure.