The 29-year-old replaces injured Ospreys forward James King.
Shingler, who has eight caps, will join the Wales squad after Scarlets' Pro12 final against Munster on Saturday.
"We've got a young squad, but we're not treating this as a development tour. We're going to the southern hemisphere to win two Tests," said Robin McBryde, Wales' head coach for the tour.
"So the selection has to reflect a balance between potential and performance, and the new players will have to reach the high levels of expectation we have of them."
Shingler's call-up comes a day after uncapped Exeter full-back Phil Dollman was summoned as a replacement for Rhun Williams.
Wales have called up Scarlets back rower Aaron Shingler for Test matches against Tonga and Samoa in June.