Dougie Fife, the 23-year-old Edinburgh winger, will win his first cap as the Dark Blues round off their Six Nations campaign at the Millennium Stadium.
He comes in for the injured Tommy Seymour on the right flank, while Castres' Max Evans takes Sean Lamont's spot on the opposite side.
Johnson announced on Wednesday that injured flanker Johnnie Beattie would be replaced by Glasgow's Ryan Wilson.
Johnson was forced to delay naming his final selection as he waited for Evans and Seymour to prove their fitness.
While the former has been given the go-ahead to win his 42nd cap, there was disappointment from Seymour as an ankle knock counted him out after his try-scoring display against France last weekend.
But Fife will now get his chance and Johnson said he was eager to see his debutant in action at Test level.
"We like Dougie's size and his competitive edge," said the Australian, who will take charge of the Scots for the final time at the Millennium Stadium.
"He chases everything, which I like, and he has shown really good glimpses playing for Edinburgh this season.
"He's been earmarked by us for a while - we've been following him for the last 12 months - and he's got his reward now. If he gets this one right, you might find that he puts a bit of pressure on (for a place) going forward, which is really good.
"I don't really think Saturday will faze Dougie. He's one of those players where it doesn't seem to matter who he marks he just goes out and plays the same."
Fife said: "I'm absolutely delighted and can't wait. The Millennium Stadium with the roof closed - I don't think it could be much better to be honest.
"When I got a run of games with Edinburgh and started doing fairly well I felt I could be on the brink (of a Scotland call) if I stuck in. Luckily, I've been patient and my time has come."