The Mexican knocked out Plant in the eleventh round to unify all four major belts in less than a year.
Canelo added Plant’s IBF belt to the WBA Super, WBC and WBO ones he had already earned over the past 11 months.
Plant put on a spirited display as Canelo struggled to pin him down, however he was finally able to floor the American twice in the eleventh - once with a left hook then again with a right uppercut.
Plant was unable to prevent the brutal assault and Canelo became victorious with a minute and five seconds of the round remaining.
Plant swiftly departed the ring after the defeat without conducting a post-fight interview, with a spokesperson informing that the 29-year-old was taken to hospital for an ‘observation’, reported by ESPN.
The win for the 31-year-old means he becomes the first Mexican and only the sixth fighter since the WBO began sanctioning world-title fights in 1988 to hold all four belts from the separate governing bodies at the same time.
Canelo’s domination began in December 2020 when he claimed the WBA Super and WBC titles after defeating Callum Smith, before he overcame Avni Yildirim in February followed by a victory over Billie Joe Saunders for the WBO honour.
What did Saul ‘Canelo’ Alvarez have to say after the fight?
Following the fight, Canelo claimed his opponent had wanted to carry on, however the Mexican told him he should stop.
Canelo said: "He wanted to continue. I told him there is no shame. Of course I came out on top.
"Caleb is a good fighter. He was a difficult opponent with a lot of ability and I do respect him.
"He was making the fight pretty difficult, but Eddy [Reynoso, trainer] told me to just stick to the gameplan in the last two rounds. In the end, I got him. That's the way it had to finish. He was already hurt and I went for the kill."
"It hasn't been easy to get to this point,” Canelo said.
"With my team I have gone really far.
"This is for everybody, especially for Mexico. We did it tonight. We are only six. It keeps me happy and motivated to be one of the six undisputed fighters in the world."