Biles dominated the final in Antwerp where she also won her first world title a decade ago, taking gold with a score of 58.399 points ahead of defending champion Rebeca Andrade of Brazil (56.766), with American teammate Shilese Jones taking bronze (56.332).
Biles, 26, also took team gold with the United States on Wednesday, less than 10 months ahead of the Paris Olympics. Her sixth world all-around triumph also gives Biles her 27th world medal.
She could extend that tally as she is still in the running for four other podiums in the apparatus finals at the weekend. The Texan has made an impressive comeback, two years after the Tokyo Olympics.
Arriving in Japan as the big favourite thanks to her four gold medals won five years earlier in Rio de Janeiro, Biles broke down and withdrew from four of the five finals.