Friday's deal was made pending a physical. Casey will give the Red Sox an experienced backup at first to starter Kevin Youkilis.
Casey, whose contract is not guaranteed, hit .296 with four homers, 30 doubles and 54 RBIs in 143 games for the Detroit Tigers last season. In 11 seasons, eight with Cincinnati, the left-handed hitter batted .301 with 130 homers and 718 RBIs.
Youkilis played 135 games at first base last season. His primary backup, Eric Hinske, appeared in 43 games but is not signed for next season. With Casey, 33, the Red Sox have a better option to shift Youkilis to third base when Mike Lowell needs a rest. Lowell, the MVP of the 2007 World Series, played in 154 games last year.
The Red Sox had been seeking a left-handed bat to come off the bench after letting lefty first baseman-outfielder Eric Hinske
become a free agent after last season. They offered a contract to
outfielder-first baseman Brad Wilkerson, but he agreed to terms
with Seattle on Thursday, preferring a chance to play regularly.
Casey was chosen for three NL All-Star teams and made a big impact with Detroit.
The Tigers obtained him at the trade deadline in 2006 and he hit just .245 in 53 regular-season games. But he hit a World
Series-high .529 with two homers and five RBIs against St. Louis,
which won the title in five games.
In 1999, his third season, Casey finished fourth in the NL in batting with a .332 average. He's been chosen for three All-Star Games, the last in 2004. He batted .312 in 2005, his last season with the Reds.
He started the next year with Pittsburgh before being traded to Detroit on July 31.
Information from The Associated Press was used in this report.