The 24-year-old Italian secured his first Paris title with a 6-4 7-6 (7-4) victory, notably without dropping a single set throughout the tournament.
Sinner extended his impressive winning streak to 26 matches on indoor hard courts, marking his fifth Masters championship and 23rd career title.
Despite Sinner's victory, Carlos Alcaraz remains the favourite to finish as the year-end World No 1, holding a 1,050-point lead ahead of the ATP Finals in Turin.
For Auger-Aliassime, the loss meant missing an automatic spot at the ATP Finals, though he advanced in the qualification standings.