Fils, 22, will be the 10th Frenchman to play in the tournament, and the first since Gael Monfils in 2016.
The world number seven joined Alexander Zverev, Carlos Alcaraz, Ben Shelton, Daniil Medvedev and Flavio Cobolli in the eight-man field.
Jannik Sinner has also qualified but will not compete due to injury, leaving two places still available.
Fils won two trophies this year - his first ATP Masters 1000 crown at the Cincinnati Open and the Barcelona Open - but missed the Australian Open and French Open due to injuries.
The ATP Finals will be held in Turin from November 15th to 22nd.
