Carroll will replace veteran Miguel Tejada, who went on the disabled list on Sunday with a calf injury.
The initial plan is to platoon Carroll, a right-handed hitter, with Chris Getz, a left-handed hitter. Getz is on the disabled list but is eligible to come off on Monday.
"Losing Miggy kind of put a hole over there for us now," manager Ned Yost said. "Jamey Carroll is pro's pro. He's a very solid player, hits left-handed pitching very well. He can play second, third and short in that order -- those are about his best positions. He'll give you a real quality at-bat."
Carroll had a .230 average in 58 games for the Twins this year. He's hitting .325 with a .372 on-base percentage against left-handers this season and has a .295 career average against lefties.
"So we'll play him at second and, on days Moose (Mike Moustakas ) needs a break, we can play him at third," Yost said. "I imagine Chris Getz will be back in the very near future, and we'll have a nice platoon at second. And we can provide opportunities to give Moose a break at third, and [Carroll] is a very proficient third baseman, too."
Yost noted that it wouldn't be a strict platoon arrangement and that Carroll likely would play some against right-handed pitchers, as well as Getz.
Carroll played for Montreal/Washington, Colorado, Cleveland and the Los Angeles Dodgers before spending the last two years with Minnesota. He's a .274 career hitter with a .351 on-base percentage. He has little home run power -- just 13 long balls in 1,261 career games.
"He's a solid guy," Yost said. "That's why you stay in this league at 39 years old because, one, you've got great work ethic. Two, you're great in the clubhouse. And three, you work hard and are still productive and he is that."
Picking up a veteran at this late stage of the season emphasizes the Royals' intent to make a run for the playoffs. After taking three of four games from Boston, the Royals are 7 1/2 games behind leading Detroit in the American League Central, and 4 1/2 games out in the Wild Card race.
Carroll not only is a versatile infielder, but he can pitch if needed. He pitched a perfect inning in relief for the Twins last Monday at the end of the Royals' 13-0 victory.
The Royals will finalize their moves on the 25-man roster prior to Monday night's game against Miami.