Martinez, who will make $19.35 million in the final year of his five-year deal, informed the Red Sox of his decision Sunday before the deadline to declare free agency.
It marks the third straight year that Martinez declined to opt out of his deal. The slugger admitted earlier this season that he was undecided about the opt-out clause, especially with the possibility of Major League Baseball adopting a universal designated hitter this winter as part of a new collective bargaining agreement.
"You learn over time in this game not to be too surprised by anything," Red Sox chief baseball officer Chaim Bloom said Sunday. "Certainly happy he's [back] with us."
After struggling during the pandemic-shortened 2020 season, Martinez bounced back in 2021, batting .286 with 28 home runs, 99 RBIs and 42 doubles -- tied for the most in the majors. The four-time All-Star also was a force in the postseason, batting .344 with three homers and 10 RBIs as Boston reached the ALCS.
"He's such a force in the lineup, not only what he produces but how he transforms what the lineup looks like around him and how he changes the conversation in the cage, the preparation before games," Bloom said. "So we're very excited he's back with us."