Mercedes driver Antonelli became the sport's youngest champion on Sunday, in only his second season, with the 20-year-old also Italy's first in 73 years.
"He's done an insane job," said Norris ahead of the race at the Autodromo Hermanos Rodriguez.
"I feel like people are somehow not giving him enough credit for what he's achieved this year.
"He's beaten a teammate (George Russell) that's been in the sport four or five times longer than him, who's also very good, and took the battle to Lewis (Hamilton)."
Antonelli, third on Sunday after starting fourth, went into the Mexico City weekend 123 points clear of Russell and 124 ahead of Ferrari's seven-time champion Hamilton.
That meant the winner of nine races so far, one more than pre-season favourite Russell has managed in his career, needed only to score two points even if either of his remaining rivals won the race.
"They (critics) say, 'Oh, he's not had much competition' and everything," continued Norris. "But that's because he just slapped his competition.
"I think he's made it look an easy year, if you can make anything look easy nowadays. I think he's done an unbelievable job. Like incredible, incredible job."
Norris won the title last year by two points from Red Bull's four-time world champion Max Verstappen, who made an amazing comeback after a season that had looked early on like being in the bag for McLaren's Oscar Piastri.
The Briton was already mathematically out of contention before the Mexico weekend and said he had realised his hopes of retaining the title had gone long before that.
Antonelli's wins include Monaco, Monza and Spa and he has smashed records along the way in a run that included five wins in a row.
Russell has won three races and been inconsistent in his form, on top one weekend and off form the next, and found it harder to adapt to the new cars and rules.
"The truth is he's been at a higher level than me this year," he said earlier in the week.