Financial terms were not disclosed but sources told ESPN that Kimbrell's deal is worth $13 million.
Baltimore has a need since All-Star closer Felix Bautista is likely out for the 2024 season after Tommy John surgery. He went on the injured list in August.
"I think both parties are entering this arrangement with the spirit of this potentially being a two-year thing. We're optimistic about it," Baltimore general manager Mike Elias said. "The plan is for him to be the closer."
Kimbrel, 35, was one of the preeminent closers of the 2010s, making seven All-Star appearances and accumulating 332 saves -- at least 68 more than anybody else -- while pitching for the Atlanta Braves, San Diego Padres and Boston Red Sox from 2011 to 2018.
The right-hander navigated that eight-year stretch with a 1.97 ERA, a 0.91 WHIP and a rate of 14.6 strikeouts per nine innings with a devastating fastball-curveball combo. He has since posted a 3.57 ERA, a 1.16 WHIP and a 13.0 strikeout rate with the Chicago Cubs, Chicago White Sox, Los Angeles Dodgers and Philadelphia Phillies.
Kimbrel made two more All-Star teams from 2019 to 2023, including this past season with the Phillies, when he posted a 3.26 ERA, saved 23 games and struck out 94 batters in 69 regular-season innings.
The sheer dominance of his 20s, however, has mostly eluded Kimbrel in his 30s. His lasting image in Philadelphia was blowing a two-run lead in the eighth inning of Game 4 of the National League Championship Series, paving the way for the Phillies' shocking elimination against the upstart Arizona Diamondbacks.
The Orioles were a major surprise last season, winning an American League-best 101 games. They won the AL East before being swept by the Texas Rangers in the division series. Many preseason projections had them finishing in the basement of the division.