The fee is expected to be worth around $3m (£2.25m) plus performance-based add-ons, says the Athletic.
The move follows Chelsea's agreement in July to sign US youth international Benji Flowers, 15, from FC Dallas under a similar arrangement once he turns 18, with Dallas set to receive an initial fee of around $3m that could rise to roughly $10m with bonuses included.
Garcia signed his first professional contract with the Galaxy as a homegrown player in January 2025, becoming the fifth-youngest player in MLS history to do so at 14 years and 198 days old.
He is due to officially join the Galaxy on an MLS contract at the start of 2027, and was included in the club's first-team squad for the first time earlier this month, remaining an unused substitute in a goalless draw with FC Dallas.
The midfielder has represented both the United States and Mexico up to Under-15 level and was called into a US Under-17 camp in June, while featuring 16 times for Ventura County FC, the Galaxy's MLS Next Pro affiliate, this season, contributing three goals and four assists.
The move fits a pattern of Chelsea investing heavily in young talent from outside Europe in recent years. The club struck a similar pre-arranged deal for Ecuadorian teenager Kendry Paez in 2023, agreeing his move at 15 with a view to him joining once he turned 18, while American internationals Caleb Wiley and Gaga Slonina have also made the switch to Stamford Bridge in recent seasons.
Garcia's signing comes amid a broader summer of recruitment at Chelsea, which has also included the arrivals of Morgan Rogers, Maxence Lacroix and Jordan Henderson to bolster the senior squad, with the club continuing to run parallel strategies of first-team reinforcement and long-term academy investment.