Operative for Starfleet Intelligence. In 2374, Chadwick supervised Miles O'Brien in an undercover operation, on the planet Farius Prime, to flush out the name of the Orion Syndicate's Starfleet informant.
O'Brien was successful in doing that, but Chadwick extended the mission when he learned that the Syndicate had developed a relationship with the Dominion. Ultimately, O'Brien and Chadwick prevented the Dominion-backed assassination of a Klingon ambassador, but at the sacrifice of Bilby, the Syndicate operative whom O'Brien had grown very close to. When O'Brien realized Chadwick had every intention of letting Bilby get killed, he slugged Chadwick in the face and went to warn Bilby.
But Bilby's fate was already sealed.