Courtesy of an injury to Alasdair Strokosch, Harley has been called up to face Italy at Murrayfield on Saturday in the Six Nations for what would be his first start for Scotland.
The 22-year-old forward has featured in eight of Glasgow's RaboDirect PRO12 clashes this season, scoring a try in the 23-14 victory over Scottish rivals Edinburgh in late December.
And after announcing himself on the international stage last year when he scored the match-winning try against Samoa off the bench on debut, Johnson expects Harley to grasp his chance with both hands.
Scotland interim head coach Scott Johnson said: "I had the pleasure of working with Robert on our tour last summer.
"He's big and aggressive and he's been knocking on the door for selection for a wee while. He deserves this chance as a reward for his club form."
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