The deal announced Monday, one day after free agent Travis d'Arnaud signed with the Atlanta Braves, includes a $4.5 million club option for 2021. The option price would increase by $250,000 each for 300, 400 and 500 plate appearances in 2020, making a second year potentially worth $5.25 million.
If the option is declined, Zunino would become eligible for free agency.
Zunino was acquired from Seattle in a five-player trade in November 2018 and started 78 of 90 games he played last season, when d'Arnaud finished the year as the team's primary catcher. Zunino hit .165 with 10 doubles, nine home runs and 32 RBIs, while throwing out 34 percent of attempted base stealers.
The 28-year-old has a .202 average with 104 homers and 273 RBIs over seven big league seasons.