The 31-year-old Irishman first broke the nose of Cerrone with his shoulder and dropped him with a high kick before striking him with several punches at the T-Mobile Arena in Las Vegas.
It was McGregor’s first win since his defeat by Khabib Nurmagomedov in 2018, and the second fastest of his career.
After his win, the professional mixed martial artist and boxer said: “I’m the first fighter in UFC history to secure a knockout victory at featherweight, lightweight and welterweight. I’m very, very happy. I’m very proud.
“I’m so happy. Who’s going up and down divisions and knocking people out like that? I’ve etched my name in history once again.
“I like this weight division, I feel really good. I don’t believe I’m there yet, though, I’ve still got some work to do to get back to where I was.”
The Irishman is expected to rake in a staggering $80 million from the fight.