Eaton signed a minor-league contract with the Red Sox on Wednesday and received an invitation to spring training, Jon Morosi of MLB Network reports.
Eaton spent the entirety of last season with the Royals' Triple-A affiliate, where he slashed .252/.299/.439 with 16 homers and 59 RBI across 460 plate appearances. A career .201 hitter in the majors, Eaton is unlikely to break camp with the big-league squad and will presumably spend most of the year at Triple-A Worcester.