He joins financial PR firm M: Communications in two weeks as a senior consultant.
D'Ancona, who set up the oil and gas PR specialist with Peter Reilly in 2002, has sold his stake to Reilly.
Reilly said M had contacted the firm through a headhunter but he decided not to take up the offer.
Before Aquila, d'Ancona and Reilly worked at former FTSE 100 oil exploration firm Enterprise Oil as IR and PR chiefs respectively.
D'Ancona will join M's IPO team to develop the agency's energy and natural resources business, which includes work for Urenco, Sibir Energy and Statoil.
Aquila's clients include Braemar Seascope, Offshore Hydrocarbon Mapping and PetroKazakhstan.
Reilly said that he wanted to expand the company's clients beyond the oil and gas sector.
The firm has poached Tulchan Communications consultant and former AIM Guide journalist William Davidson, and Hanson IR executive Yvonne Bate.