UFC officials confirmed the news to ESPN.com on Tuesday following an initial report by MMAFighting.com.
The United States Anti-Doping Agency (USADA) also confirmed it was aware of Lesnar's retirement. Because of the retirement, Lesnar is no longer included in USADA's testing pool under the UFC's anti-doping program.
Last month, Lesnar, 39, was handed a one-year suspension from the USADA because of a pair of failed drug tests in 2016. The Nevada State Athletic Commission also suspended Lesnar for one year. The suspensions do not affect his professional wrestling career in WWE.
Lesnar would have been eligible to return to active competition in July, but his USADA suspension freezes with this announcement. Should Lesnar (5-3) opt to resume his UFC career at any point, he would be required to fulfill the remaining five months of that suspension.
Lesnar has not commented publicly on his retirement.
A former NCAA Division I national champion wrestler, Lesnar came out of a nearly five-year retirement to face Mark Hunt at UFC 200 last July in Las Vegas. Lesnar won the fight via unanimous decision, but it was later changed to a no-contest after the positive tests were revealed.
Lesnar tested positive for clomiphene, an estrogen blocker. He denied knowingly taking the banned substance.