The deal is worth a guaranteed $2 million with another $1 million available in incentives, Jon Heyman of MLB Network reports.
Harrison is expected to serve as the Tigers' everyday second baseman, according to Rosenthal. While he's primarily played second over the past three years, he's got experience at third base, shortstop, and the outfield - skills that manager Ron Gardenhire could put to use if necessary.
The versatile 31-year-old is coming off an injury-plagued season in which he posted a .250/.293/.363 slash line with eight homers, 22 extra-base hits, and three stolen bases over 97 games for the Pittsburgh Pirates. While those numbers represent one of the worst showings of his career, Harrison is just one year removed from slashing .272/.339/.432 with 16 homers during an All-Star campaign.
In Detroit, he'll get a chance to rediscover that form and perhaps boost his midseason trade value for the rebuilding Tigers. Harrison will also have a familiar face alongside him in shortstop Jordy Mercer, his longtime double-play partner in Pittsburgh.
Over eight seasons with the Pirates, Harrison is a .277/.317/.408 hitter with 773 hits, 52 homers, 269 RBIs, and 75 steals.