Varitek, 39, broke into the majors in 1997 and spent his entire career with the Red Sox. He is the club's all-time leader in games caught (1,488).
The switch-hitting backstop helped Boston end its 86-year World Series title drought in 2004 and was the starting catcher for the Red Sox when they won captured the championship again three years later.
Varitek hit just .221 in 68 games last season, finishing with 11 home runs and 36 runs batted in. He is a career .256 lifetime hitter with 193 homers and 757 RBI.