Nurmagomedov, 30, submitted America’s Poirier in the third round on Saturday to make it 28 wins from 28 fights.
The Russian outwrestled Poirier over the first two rounds before securing a rear naked choke to cement his status as the UFC’s number one 155lb fighter.
Numagomedov defeated Conor McGregor via submission at UFC 229 in 2018.
After serving his ban, the Russian returned to face Poirier with the well-deserved reputation as one of the most dominant fighters in the world.
Poirier had captured the interim title with a thrilling win over current featherweight champion Max Holloway at UFC 236 in April.
In what has been one of the most hotly anticipated fights in recent years, Dagestani-born Khabib was looking to re-establish himself as one of the biggest names in the sport, following his nine-month suspension for his part in the UFC 229 aftermath.