South Africa have rested several of their leading players for the quickfire series, which will be followed by five One-Day Internationals in the build-up to the Cricket World Cup that starts in India on October 8.
Stubbs is usually a handy spin option with the ball but will don the gloves in the absence of rested Quinton de Kock.
"Tristan will keep wicket," Markram said on Tuesday. "He has been working really hard the last couple of weeks. He is a guy who will never leave a stone unturned. He has spent hours and hours working on his keeping.
"I think it adds another element to his game to take forward in his cricketing journey. We have seen him do well with the ball, we all know what he can do with the bat and now he has got the gloves, so he is an all-dimension player."
Keshav Maharaj is back playing after rupturing his Achilles tendon in March, though he will not be in the team for Wednesday's game.
"It is fantastic to see him back on the park," Markram said. "It has been a tough journey for him, but he has been incredibly committed and motivated to get ahead of schedule in terms of his recovery."
South Africa have included precocious batting talent Dewald Brevis among several new faces in the squad, with De Kock, Heinrich Klaasen, David Miller, Anrich Nortje and Kagiso Rabada all rested.
"It is a newer and less experienced group, but we are here to win," Markram said. "It is a great opportunity for us as a slightly younger team to take on a very good Australian side.
"There might be errors made on the night, but we are not too worried about that."
Markram says South Africa will not use their missing players as an excuse if things do not go to plan in the series.
"It is about two teams that really enjoy playing against each other, respect each other and play the game nice and tough," he said. "We have a way we want to play and it is about giving guys the freedom to do that.
"We won't use inexperience as an excuse, we believe everyone here can win games for South Africa."
