Martinez will start at designated hitter and bat fifth in Friday's game against the Cardinals.
It will be Martinez's Mets and season debut after he was sent to the minors for a while following a late-March signing. The 36-year-old will be given extra days off in the early going as he gets his feet under him, but Martinez will eventually be the team's everyday DH. He slashed .271/.321/.572 with 33 home runs for the Dodgers last season.