The third baseman was recently named a Texas League All-Star after leading the league in several offensive categories.
Headley, a switch-hitter, led the Texas League in batting average (.357), on-base percentage (.433) and slugging percentage (.648) while ranking second in RBIs (42). He also led the Missions with 45 runs, 81 hits, 21 doubles and 13 homers.
Padres vice president of scouting and player development Grady Fuson gave Headley the news before batting practice on Thursday.
Headley came into the year with a .282 career batting average with 47 doubles, 18 homers and 107 RBIs in 190 games.
Headley will be put on the 40-man roster. Paul McAnulty was optioned to Triple-A to make room for Headley.
Brett Bonvechio will take Headley's spot on the San Antonio roster.
MadFriars.com talked to Headley after he received the call and will have an interview with him later tonight.