He has played in Major League Baseball (MLB) for the Miami Marlins and Los Angeles Dodgers. Prior to his baseball career, he was a short track speed skater and baseball player who represented the United States and medaled at the 2014 Winter Olympics and 2020 Summer Olympics. He is the sixth athlete and third American ever to medal in both the Summer and Winter Olympics in different disciplines. After his MLB debut on August 5, 2020, Alvarez became the first Winter Olympics athlete and the first non-baseball Olympian since Jim Thorpe to play Major League Baseball. Only Alvarez and Jim Thorpe have played Major League Baseball and won an Olympic Medal in another sport.
On September 8, 2024 the Boston Red Sox traded him to the New York Mets.