The 22-year-old impressed in last weekend’s win over Australia and will again start ahead of Jack Crowley.
Ireland have Garry Ringrose returning from injury to partner Bundee Aki in the centres, with Andrew Porter and Josh van der Flier also back in the starting forward pack.
South Africa's Rassie Erasmus has recalled several established starters, including Sacha Feinberg-Mngomezulu at fly-half, for the crucial match.
RG Snyman is set to earn his 50th cap for South Africa, providing lock cover from the bench.