The New York Mets selected Alonso in the second round, with the 64th pick overall, of the 2016 Major League Baseball draft.
He signed with the Mets for a $909,200 signing bonus, and spent 2016 with the Brooklyn Cyclones of the Class A-Short Season New York-Penn League, where he posted a .322 batting average with five home runs and 21 RBIs in thirty games.
He was chosen to participate in the league's All-Star Game.
He began the 2017 season with the St. Lucie Mets of the Class A-Advanced Florida State League, and after batting .286 with 16 home runs and 58 RBIs in 82 games, was promoted to the Binghamton Rumble Ponies of the Class AA Eastern League in August, where he batted .311 with two home runs and five RBIs in 11 games.

MLB.com ranked Alonso as New York's fourth best prospect going into the 2018 season.
He began the 2018 season in Binghamton, and received a midseason promotion to the Las Vegas 51s of the Class AAA Pacific Coast League.
He represented the Mets in the 2018 All-Star Futures Game.
In 132 games between Binghamton and Las Vegas, he slashed .285/.395/.579 with 36 home runs and 119 RBIs.
He won the Joe Bauman Home Run Award.
 That season, Alonso was the final batter in Cashman Field history, as he hit a walk-off home run in the bottom of the 9th inning during the last baseball game played at the facility.
The New York Mets selected Alonso in the second round, with the 64th pick overall, of the 2016 Major League Baseball draft. He signed with the Mets for a $909,200 signing bonus, and spent 2016 with the Brooklyn Cyclones of the Class A-Short Season New York-Penn League, where he posted a .322 batting average with five home runs and 21 RBIs in thirty games. He was chosen to participate in the league's All-Star Game. He began the 2017 season with the St. Lucie Mets of the Class A-Advanced Florida State League, and after batting .286 with 16 home runs and 58 RBIs in 82 games, was promoted to the Binghamton Rumble Ponies of the Class AA Eastern League in August, where he batted .311 with two home runs and five RBIs in 11 games.
MLB.com ranked Alonso as New York's fourth best prospect going into the 2018 season. He began the 2018 season in Binghamton, and received a midseason promotion to the Las Vegas 51s of the Class AAA Pacific Coast League. He represented the Mets in the 2018 All-Star Futures Game. In 132 games between Binghamton and Las Vegas, he slashed .285/.395/.579 with 36 home runs and 119 RBIs. He won the Joe Bauman Home Run Award.  That season, Alonso was the final batter in Cashman Field history, as he hit a walk-off home run in the bottom of the 9th inning during the last baseball game played at the facility.
Pete Alonso