The Mets also reached agreements with 12 other players on one-year deals that avoided arbitration, leaving only right-hander Chris Bassitt without a deal before the deadline to exchange proposed salaries.
Alonso, 27, received a significant raise in his first year of arbitration eligibility, coming off a season in which he led the Mets in every major batting category: hits (147), home runs (37), RBIs (94), batting average (.262) and on-base percentage (.344).
Bassitt, 33, was acquired from Oakland this month. He was 12-4 with a 3.15 ERA in 27 starts last season.
The other players agreeing to deals were infielders Jeff McNeil ($3 million) and J.D. Davis ($2.76 million), catcher Tomas Nido ($890,000), and pitchers Seth Lugo ($3,925,000), Trevor Williams ($3.9 million), Miguel Castro ($2.62 million), Joey Lucchesi ($1.15 million), Luis Guillorme ($875,000) and Drew Smith ($750,000).
The Associated Press contributed to this report.