The make-up matchup was announced on Wednesday’s episode of “UFC Tonight.”
Duffy was pulled from Saturday’s main event at the last-second after the UFC discovered he had suffered a mild concussion during training the weekend prior.
Poirier was paid his show money for making the trek to Dublin.
Since losing to Conor McGregor, Poirier has found his stride back up at the lightweight division. “Diamond” has rattled off two straight wins after leaving the featherweight class, most recently TKO’ing Yancy Medeiros in June.
Duffy will be riding a four-fight winning steak into the tango. “Irish Joe” has posted two consecutive first round finishes since joining the UFC.