In exchange, the Red Sox acquired a pair of prospects from San Diego, outfielder Jeisson Rosario and infielder Hudson Potts.
Moreland adds even more power to an already explosive San Diego lineup.
The Padres are making one move after another in pursuit of their first playoff appearance in 14 years. On Saturday, they bolstered their bullpen by acquiring Trevor Rosenthal in a trade with the Kansas City Royals.
Moreland, who turns 35 on Sept. 6, was leading the Red Sox with eight homers, 21 RBI and a .328 batting average. He’s made 19 starts at first base this season and three more as a designated hitter.
Originally a 17th round pick by Texas in 2007, Moreland is hitting .253 over his career with 174 homers and 491 RBI. He has been on teams that have made the playoffs in seven of the last 10 seasons, including the World Series champion Red Sox in 2018.
The left-handed slugger earned his first All-Star Game selection in 2018. He was a Gold Glove winner at first in 2016.
Moreland reached 10 years of major league service on Saturday.