The 34-year-old three-time All-Star selection posted a .200/.210/.283 slash line with one home run across 20 appearances before getting let go by the Reds.
Cincy acquired him in a December trade following a strong bounce-back season with the Los Angeles Dodgers in 2018. He compiled a .819 OPS with 21 homers in 146 games for L.A.
Although the veteran outfielder has enjoyed a majority of his success with Los Angeles, he refused to lament his offseason move to Cincinnati.
"It's a business. I can't be disappointed," Kemp told reporters in March. "I've still got a jersey on. I'm just happy to be playing baseball."
He struggled with the Reds, however, and landed on the injured list in late April with a broken rib.
Kemp will now attempt to earn a role with a Mets club that features four outfielders on the IL: Yoenis Cespedes, Michael Conforto, Brandon Nimmo and Jeff McNeil.
He'll likely start with the Triple-A Syracuse Mets in what will be a combination of rehab from his rib injury and a proving ground after signing a minor league deal. He could be called up to provide depth at the corner outfield spot if he shines in Syracuse.