Jankowski, who turned 24 in June, will be in uniform on Wednesday as the Padres conclude a three-game series with the Braves at Petco Park.
Jankowski, who was the 44th overall pick in the 2012 Draft out of Stony Brook University, was having a monster season between two Minor League affiliates. He was hitting .335/.413/.425 with 32 steals this season between Double-A San Antonio and Triple-A El Paso.
"He put himself on our road map and made it easier to make this call," Preller said. "He earned his way up, for sure."
In parts of four seasons, Jankowski is hitting .293/.360/.369 with 137 stolen bases.
Jankowski, a left-handed hitter, could find himself in a platoon situation in center field with Melvin Upton Jr.
"We're not going to let him come up and sit on the bench," Preller said.
This could essentially serve as an audition for 2016 for Jankowski.
The Venable trade landed San Diego a 20-year-old catcher in Marcus Greene and a player to be named, which will likely be the primary piece of the deal.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.