The woeful Orioles, owners of baseball's worst record (31-70), receive minor league pitching prospect Wynn Pelzer in exchange for the 36-year-old Tejada, who is hitting .269 with seven homers and 39 RBIs.
Tejada, who has played both shortstop and third base in a 14-year career that has included two stints in Baltimore along with stops in Oakland and Houston, gives the Padres some power at the plate and options defensively.
While Tejada's seven home runs are on pace for a career low, he has 292 career homers and has hit more than 20 eight times.
Tejada is a six-time All-Star who won the 2002 MVP award when he hit .308 with 34 home runs and 131 RBIs for Oakland.
(Writing by Steve Keating in Toronto, Editing by Steve Ginsburg)