Les Bleus head to Rome for the first game of their title defence, after they completed the Grand Slam last year.
Dumortier, 22, is Lyon's top try scorer in the Top 14 this season and his fine form has seen him make Galthie's selection in the place of Gabin Villiere, who sustained a fractured fibula.
With Jonathan Danty also injured, Gael Fickou and Yoram Moefana have been named as centres. Damian Penaud will play on the right wing, with Dumortier on the opposite flank.
Romain Ntamack and captain Antoine Dupont will be paired together in the halves, while Nolann Le Garrec could make his debut from the bench.
"We finished second twice in a row before winning it with a Grand Slam but our journey is not finished," Galthie said.
"We are going to get better because our team has not yet reached the age of maturity."
Italy has also confirmed its starting XV. It won five Tests across 2022 – a 45 per cent win ratio – its highest in a calendar year since 2007, and its best in a non-Rugby World Cup year since 1998. That included a first ever victory over Australia.
The Azzurri took the wooden spoon in last year's Six Nations, but did end a run of 36 straight defeats in the tournament by defeating Wales.
Full-back Ange Capuozzo impressed on his Six Nations bow last year, going over twice against Scotland.
Capuozzo went on to be named World Rugby's men's Breakthrough Player of the Year, and he gets a start against Les Bleus.
Monty Ioane's injury is a blow for coach Kieran Crowley, who has named Tommaso Menoncello and Pierre Bruno on the flanks.
Michele Lamaro will captain the side. He made 86 tackles in last year's Six Nations, 16 more than second-best Hamish Watson.
Italy team: Ange Capuozzo, Pierre Bruno, Juan Ignacio Brex, Luca Morisi, Tommaso Menoncello, Tommaso Allan, Stephen Varney; Lorenzo Cannon, Michele Lamaro, Sebastian Negri, Federico Ruzza, Niccolo Cannon, Simone Ferrari, Giacomo Nicotera, Danilo Fischetti.
Italy replacements: Luca Bigi, Federico Zani, Pietro Ceccarelli, Edoardo Iachizzi, Giovanni Pettinelli, Manuel Zuliani, Alessandro Fusco, Edoardo Padovani.
France team: Thomas Ramos, Damian Penaud, Gael Fickou, Yoram Moefana, Ethan Dumortier, Romain Ntamack, Antoine Dupont; Gregory Alldritt, Charles Ollivon, Anthony Jelonch, Paul Willemse, Thibaud Flament, Uini Atonio, Julien Marchand, Cyril Baille.
France replacements: Gaetan Barlot, Reda Wardi, Sipili Falatea, Romain Taofifenua, Thomas Lavault, Sekou Macalou, Nolan Le Garrec, Matthieu Jalibert.