Boston receives Kinsler and cash considerations in exchange for pitching prospects Ty Buttrey and Williams Jerez. The teams announced the deal on Monday night.
Kinsler, 36, is hitting .239 with 13 home runs and 32 RBIs this season. The four-time All-Star hit .236 with 22 home runs and 52 RBIs in 2017 for the Detroit Tigers. Kinsler played his first eight seasons for the Texas Rangers, before joining the Tigers in 2014. He has an $11 million salary in 2018 and is a free agent next season.
Buttrey was Boston's No. 19 prospect, according to MLB Pipeline. The 25-year-old right-handed pitcher had a 2.25 ERA, a 1-1 record and one save in 32 appearances this season for the Triple-A Pawtucket Red Sox. Jerez, 26, had a 2-1 record, 3.63 ERA and five saves in 34 games for Triple-A Pawtucket.
"We're very happy to get Ian," Red Sox president of baseball operations Dave Dombrowski told reporters. "We also got cash considerations in the deal. Very happy. We were looking at trying to upgrade our club any way we possibly can. He's been playing extremely well for an extended time period. He's been hitting well. He's a winning-type player. He's a very good defensive player, still has good instincts.
"We think he makes us a better ball club, because he goes into second base and is in a spot where he can play basically every day. He's a good offensive player and a good defensive player, so we think he makes us a better club."
Red Sox second baseman Dustin Pedroia has played in just three games this season after undergoing knee surgery. Boston has used Eduwardo Nunez and Brock Holt to cover the position in Pedroia's absence, before the trade for Kinsler.