The way Boston's roster is constructed, the bench will consist of a backup catcher, outfielder Chris Young and either Brock Holt or Pablo Sandoval, depending on who becomes the starting third baseman.
That leaves one more opening, and Rutledge will likely compete with left-handed-hitting Marco Hernandez for the 25th spot.
"It was interesting, because we did try to re-sign him and we always had a good relationship with him and we liked him," said Red Sox president of baseball operations Dave Dombrowski. "It was a situation for us, we looked at our club, we thought we might need a right-handed utility infielder and we like what he can do for our ballclub and he was an obvious choice for us.