The Padres received cash considerations in the deal.
The 32-year-old Loney has been in Triple-A this season after signing a minor league deal with San Diego during the offseason. Loney had an opt-out clause in his contract, and had he not been traded, he would have likely landed with the Mets anyway.
Ever since starting first baseman Lucas Duda went on the disabled list on May 21 with a lower back stress fracture, the Mets have been on the lookout for a viable replacement.
In his absence, the team turned to Eric Campbell at first base, who is hitting .182/.303/.255 on the year in 66 plate appearances.
Loney has been hitting well with Triple-A El Paso, posting a .342/.373/.424 triple-slash line with two home runs and 28 RBIs over 169 plate appearances.
Loney was last in the Major Leagues in 2015 with the Rays, but was released the end of the season after hitting just .280/.322/.357 with four homers and 32 RBIs in 388 plate appearances. He was worth -1.3 FanGraphs Wins Above Replacement (fWAR).
With the Mets, Loney will likely start at first until Duda returns to action.