Sullivan will start at catcher and bat ninth in his MLB debut Tuesday against Atlanta.
The 29-year-old could get a handful of starts behind the plate for the Padres while Luis Campusano recovers from a left thumb sprain. Campusano was placed on the 10-day injured list Monday and Austin Nola is on the bench Tuesday. Sullivan was sporting an .800 OPS with one home run and three stolen bases through nine games this season at Triple-A El Paso.