The 23-year-old led every lap to secure the title.
Chadwick, 23 from Bath headed into the season finale with a 10-point advantage over compatriot Alice Powell following her victory on Saturday.
And after a blistering start, she led every lap to secure the title, and claim the 500,000 US dollar (£363,000) prize pot.
Powell failed to trouble her rival, starting ninth before taking the chequered flag in sixth.
Chadwick, an academy driver for the Williams team, won the first instalment of the all-female championship in 2019.
Last year’s series was cancelled amid the coronavirus pandemic, with all of this term’s eight-race calendar featuring on Formula One’s undercard.
Det har vært 45 years since a female driver, the Italian Lella Lombardi, last competed in an F1 race.
But Chadwick’s triumph will see her awarded with 15 points on her super licence.
Forty points are required over a three-year period to take part in a grand prix, og 25 needed to participate in a practice session.