Hosmer dealt to Red Sox after reportedly rejecting trade to Nats
Boston also got prospects Max Ferguson and Corey Rosier, while left-hander Jay Groome was dealt to the Padres in return.
San Diego will pay down a significant portion of Hosmer's remaining contract, sources told Jeff Passan of ESPN.
Hosmer heads to Boston after reportedly rejecting a trade to the Washington Nationals as part of a deal for Juan Soto earlier Tuesday.
The 32-year-old owns a .272/.336/.391 slash line with eight homers, 16 doubles, and 40 RBIs in 90 games this season. He should help improve first base for the Red Sox, as Boston's first basemen have combined for minus-1.1 WAR and 75 wRC+ this campaign, according to FanGraphs.
Hosmer signed an eight-year, $144-million deal with San Diego before the 2018 season. It was the largest contract in Padres history at the time.
The four-time Gold Glover hit .265/.325/.411 with 69 homers and 309 RBIs during his Padres tenure. He won a World Series with the Kansas City Royals in 2015.
Hosmer's acquisition is the latest move Boston's front office has made in recent days. The Red Sox traded catcher Christian Vazquez and left-hander Jake Diekman while acquiring outfielder Tommy Pham and catcher Reese McGuire on Tuesday.
Meanwhile, Groome is the No. 13 prospect in the Red Sox system, according to Baseball America. The former first-rounder owns a 3.52 ERA with 9.5 K/9 in Double-A this season.
Ferguson and Rosier aren't top-20 prospects in the Padres' organization.