The Mercedes driver sealed the Drivers' Championship in Mexico, finishing third to end the slim hopes that George Russell and Lewis Hamilton, his last remaining challengers, had of catching him.
In a race full of drama and incidents, including a full red flag and a safety car, the Italian kept his nose clean to finish on the podium behind former world champions Max Verstappen and Hamilton.
His teammate Russell finished in sixth, in what has turned out to be a miserable campaign for the British driver.
On his radio after the race, he was emotional when talking to his race engineer Pete Bonnington, and celebrated inside the stadium on the track.
Speaking to Nico Rosberg, another world champion with Mercedes, after the race, he said: "We did it. Without my family and Mercedes, I wouldn't be here. This moment will live forever.
"It's been an incredible season."
As a result, he's broken the record set by Sebastian Vettel in 2010, when the German became F1's youngest title winner at the age of 23.
The victory in Austin a week ago was Antonelli's ninth in a season in which he's been the man to beat since the second round in Shanghai.
There, he claimed the first win of his F1 career, and he then went on to claim four consecutive victories to put daylight between himself and teammate Russell, the man widely expected to lift the title at the start of the season.
Numerous further victories and podiums followed in the summer and autumn, and while a fair bit of misfortune for Russell played a part in Antonelli remaining a long way ahead in the standings, the Italian has had the beating of the Brit throughout the year.
The title triumph is the culmination of a remarkable rise for a man who headed into 2026 having never won an F1 race and hadn't driven an F1 car competitively prior to 2025.
Mercedes team boss Toto Wolff was always certain he had a generational talent on his hands, as he made clear when he chose Antonelli over a number of more experienced drivers when replacing seven-time world champion Hamilton for the 2025 campaign.
Many questioned the Austrian's judgement when his prodigy made a shaky start to his F1 career, making costly errors and crying in front of cameras after a poor qualifying performance in Belgium.
However, it was clear from the start of this year that the Italian had stepped up his game massively, and thanks to blistering pace, relentless consistency and remarkable composure in the face of immense pressure, he's put together one of the best campaigns a young talent has ever driven.
That's led to him becoming F1's youngest champion ever, Italy's third, and the nation's first since 1953.