With one-day skipper Pat Cummings sidelined by a fractured wrist but expected to return for October's World Cup, Marsh will lead Australia in three Twenty20 and five 50-over matches against South Africa, starting next week.
Left-arm quick Johnson, power-hitter Matthew Short and left-arm seamer Aaron Hardie have all earned maiden national call-ups.
Marsh said Johnson, 27, had hit form after a series of injuries earlier in his career.
"We haven't seen much of him because he's had a lot of injuries and he sort of burst onto the scene last year," Marsh told reporters. "He's an incredible talent.
"I faced him in a one-day final and was blown away by his skill and pace, so I think he's going to feel right at home."
Marsh said Short and Hardie will also have chances to stake claims for places at the 50-over World Cup in India.
Cummins will take over as ODI captain when Australia arrive in India ahead of the World Cup. Test vice-captain Steve Smith is also out of the South Africa trip with a wrist injury.
All-rounder Marsh said he won't "try and reinvent the wheel" while in charge, having gained experience captaining Western Australia.
"I'm just looking forward to the opportunity. We'll get through South Africa and see how we go, I am available to captain for as long as the team needs me," he said.
