Helwani noted Poirier signed the pact last week.
McGregor and Poirier met for the first time at UFC 178 in 2014. McGregor won by first-round technical knockout to improve to 16-2 at the time.
The 32-year-old McGregor last fought at UFC 246 in January, beating Donald "Cowboy" Cerrone by first-round TKO to improve to 22-4.
McGregor retired from the UFC after that fight and has since teased getting back into boxing for a bout with Manny Pacquiao, but it was widely assumed he would return to the UFC at some point, just as he did after a previous retirement.
The Irishman had been vocal about wanting a rematch with Khabib Nurmagomedov after losing to Khabib by fourth-round submission at UFC 229. But with Khabib retiring after his win over Justin Gaethje at UFC 254 last month, McGregor turned his attention to Poirier.
While Poirier was overmatched against McGregor the first time they met, the 31-year-old veteran has enjoyed much success since that loss.
Poirier is 26-6 with one no-contest in his career, and since losing to McGregor, he's 10-2 with one no-contest.
Over his past eight fights, Poirier has lost only once, a third-round submission defeat at the hands of Khabib at UFC 242 last year.
In his most recent fight, Poirier beat Dan Hooker by unanimous decision at UFC on ESPN 12 in June.
Barring a Nurmagomedov comeback, four fighters stand out as strong candidates to vie for his lightweight title. The UFC rankings list Gaethje, Poirier, Tony Ferguson and McGregor as the top four fighters in the division, in that order.
Because of that, all signs indicate the winner of McGregor vs. Poirier will earn a shot at the UFC lightweight title in their next fight.