The 15-year-old has put pen to paper on a contract running until 2029.
Gomis joins Leipzig from FC Metz, for whom he had been playing in the Under-19s.
The centre-forward has already represented France at Under-16 level, making eight appearances and scoring once for his country.
Metz had hoped to hand Gomis his first professional contract, but the striker turned down the offer to move to Germany instead.
The decision represents a significant blow for the Ligue 2 club, who regard Gomis as one of the biggest talents in their academy.
RB Leipzig's willingness to move for a player so young underlines the growing trend among Bundesliga clubs to identify and secure elite teenage talent well before they reach senior football.
The Sachsen faithful will now hope Gomis can follow the path of previous academy graduates who progressed through Leipzig's youth pathway into first-team contention in recent years.
For now, Gomis will continue his development in Leipzig's youth setup as he adapts to life in German football at just 15 years of age.
His move continues a pattern of German clubs targeting young talent from the French leagues, where Ligue 2 and Ligue 1 academies have produced a string of promising forwards in recent seasons.