The Major League Soccer side will pay nearly $5.9 million (€5m) to bring in the 21-year-old forward.
Cabral has been one of the revelations of the season for Valenciennes, with the Paris Saint-Germain academy product signing a contract with the Galaxy through 2026.
Cabral left the PSG academy on a free for Valenciennes in 2017, where he gained more opportunities to play with the first team. He impressed for his first full season with 10 goals and five assists in 32 games across all competitions.
He is a quick and skilful left winger with a great understanding of the game. He impressed Jovan Kirovski, the Galaxy's technical director, who has been scouting the French market in search of young talents. The Galaxy beat a few other clubs in Ligue 1 and the Bundesliga to sign the highly-rated winger.
Cabral is expected to join his new team in the next few days as the Galaxy prepare for their season opener on April 18 at Inter Miami CF. Should he feature in that game, he'll be going against compatriot Blaise Matuidi, who Cabral would watch play during their time together with the PSG ranks.