The Reds agreed to a major-league contract with Smith on Thursday, Jeff Passan of ESPN.com reports.
The 29-year-old was recently cut loose by the Red Sox following the return of Triston Casas from injury, but he's managed to quickly land another major-league deal. Smith slashed just .237/.317/.390 in 83 games for Boston, although he has a respectable .747 OPS since the All-Star break. Smith could see some action at first base while Jeimer Candelario (toe) is out.