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.

The result marks a 5% rise on cash profits from a year earlier.
The lender also said its after-tax profit rose $A3.5bn during the period, up 3% from a year earlier.
The cash profit number strips out some one-off items and is the bank's preferred measure of performance.
Forecasts were for a rise in cash profit to A$3.6bn for the period.
Analysts said the results were a "welcome relief" as Australia's economy continues to face slowing growth and after rival Westpac bank posted disappointing results on Monday.
ANZ's chief executive Mike Smith said the results were "well balanced" and that progress had been made in reshaping the lender's business in a "more challenging macro-environment".
But Mr Smith noted the lender would be operating in a "lower growth environment" in the future, "in which there will continue to be occasional volatility and shocks".
The bank's positive half-yearly performance numbers come as Australia's central bank meets later today to decide whether to cut interest rates to an historic low.
Analysts said investors seemed to like the latest numbers from the lender as the stock was up as much as 3.9% following the announcement.
"The result from ANZ will be taken favourably, with cash earnings modestly above consensus," said Melbourne-based Chris Weston from IG Markets.
"The result itself was of a better quality than Westpac," he said, "although investors will take little heart from either bank's capital position."
Michael McCarthy of CMC Markets in Sydney said ANZ's results were "a welcome relief" after Westpac's flat result on Monday.
ANZ and Westpac are among the top four banks in Australia, together with National Australia Bank and Commonwealth Bank.
ANZ is the nation's third biggest bank by market value.
Australia's banking sector, particularly the so-called top four, is regarded as being highly profitable. The country's big lenders made it through the global financial crisis relatively unscathed.
Wales have called up Scarlets back rower Aaron Shingler for Test matches against Tonga and Samoa in June.
[NEXT_CONCEPT]
One of Australia's biggest lenders, ANZ, has beaten expectations and posted a half-year cash profit of 3.7bn Australian dollars ($2.9bn;£1.91bn) in the six months ending in March.