The Mets selected Jankowski's contract from Triple-A Syracuse on Wednesday, Tim Healey of Newsday reports.
Manager Buck Showalter confirmed earlier in the day that Jankowski would be joining the Mets for Opening Day, but the 30-year-old outfielder wasn't officially added to the 40-man roster until the Mets placed newly-signed reliever John Curtiss (elbow) on the 60-day injured list in a corresponding move. Jankowski's patient eye at the plate, good speed and ability to defend three outfield spots should make him a quality bench piece for the Mets, but it'll likely take absences from at least two of Brandon Nimmo (neck), Starling Marte, Mark Canha and Dominic Smith for him to pick up regular starts.