Jon Heyman of Fancred first reported the signing Friday. Terms of the deal haven't been announced.
The Mets will be Jackson's third team of the 2018 season. He signed with the San Francisco Giants in January before getting traded to the Texas Rangers on July 8. The Rangers released him less than a week later.
The 31-year-old Texas native posted a lackluster .242/.309/.295 triple-slash line with no home runs in 59 games for the Giants prior to the trade. He didn't appear in any contests for the Rangers.
In March, Jackson discussed being prepared to fill any role with San Francisco:
"You can control what you can control. I think that's something over time that I started to accept. But the same time I will not change who I am as a player and as a person, and continue to do the things that I've always done no matter where I am in the lineup or in the field. Just try to keep your focus and be ready. ... It's all about being ready and keeping that mindset."
The outlook with the Mets will be similar. He'll provide outfield depth for the rest of the year with Yoenis Cespedes set to undergo season-ending surgery on his heels.
Jackson will likely split time in center field with Brandon Nimmo, who's also been getting starts in right field, and Matt den Dekker, at least until a hot hand emerges.