The United States Anti-Doping Agency confirmed Lesnar's re-enrollment into the program on Monday. The news was first reported by MMAFighting.com.
"After receiving notice of his intent to compete in the UFC, Brock Lesnar re-entered the testing pool on July 3," USADA officials stated. "With six months and four days remaining on his period of ineligibility, Lesnar will be able to compete on or after January 8, 2019, should he remain in compliance with the UFC Anti-Doping Policy."
Lesnar, 40, attended UFC 226 last weekend in Las Vegas, where Cormier knocked out Stipe Miocic in the first round to win the heavyweight title.
Lesnar and Cormier squared off immediately afterward, and UFC president Dana White told ESPN that the fight is "definitely happening."
Per the UFC's anti-doping policies, any athlete coming out of retirement is required to enroll in the program for six months prior to competition. Lesnar is also serving a suspension he received in 2016 for failing multiple drug tests around a performance at UFC 200.
The professional wrestling superstar is also a former UFC champion. He won the title in 2008 and recorded two successful title defenses.
Cormier (21-1) has said he plans to retire by his 40th birthday in March 2019. He intends to face Lesnar early next year and has left the door open to face another opponent in the second half of 2018 as well.