Born in Los Angeles, California, Álvarez signed with the LA Galaxy II of the United Soccer League on August 2, 2017. In signing with the side, Álvarez became the youngest signing in USL history, ahead of the previous holder Alphonso Davies, at 15 years, one month, and 14 days. He made his first appearance for LA Galaxy II on September 9, 2017 when he was on the bench against San Antonio FC. Álvarez made his professional debut for LA Galaxy II on October 7, 2017 against Portland Timbers 2. He came on as a 46th-minute substitute for Adrian Vera as LA Galaxy II won 3–2. In playing, Álvarez became the youngest player to ever play a USL match. Álvarez was moved to parent club LA Galaxy ahead of their 2018 season, but was loaned back to the reserve team. Álvarez made his senior team debut on March 2, 2019, and assisted on a goal during a 2–1 victory over the Chicago Fire.
International career
Álvarez is eligible for the United States and Mexico, having been born in the United States to Mexican parents. He currently represents Mexico at youth level after playing for the United States at youth level, and has stated "I'm not closing the door on anyone. I could still play for the U.S. or I could keep playing for Mexico. But I'm with Mexico right now and that's my focus." Álvarez originally represented the United States U15s. In April 2016, he served as their captain at the 2016 International Festival of Fútbol in Rosario, Argentina, starting all three matches and leading the United States to the title. In the opening match against Talleres de Córdoba, Álvarez scored three goals and assisted two more goals in a 5–1 victory. He also scored against Uruguay U15s in a 2–0 win. In June 2016, Álvarez was again called to the United States U15s, for a four-team tournament in Zagreb, Croatia in which he made one start against Croatia U15s. Álvarez then switched to represent Mexico U15s in September 2016. He scored a brace for them in a friendly 7–0 win over the Cayman Islands U17 on 11 August 2017. He also represented the Mexico U15s in their championship-winning run at the 2017 CONCACAF Boys' Under-15 Championship, and provided the game-winning assist against his former team, the United States U15s. Álvarez debuted for the Mexico U17s in a 1–0 win over the Argentina U17s, and scored the only goal in the match. He was included in the roster that would participate at the 2019 U-17 World Cup. He scored four goals in the tournament, scoring the winning goal from a free-kick in the semi-final against the Netherlands as Mexico finished runner-up against Brazil.
