The former Falkirk Rugby Club player, now with French side Racing 92, is one of six Scottish stars in the 23-man squad this weekend which sees international teammate Stuart Hogg wearing the captain’s armband.
Hamish Watson, Chris Harris and Ali Price also make the Starting XV with Zander Fagerson on the bench.
"It’s good to have arrived in Johannesburg and get the Tour underway," said Lions Head coach, Warren Gatland
"We had a pleasing win last week up in Edinburgh, but there’s still plenty we need to get right on Saturday.
"I’ve been encouraged by the way the boys have trained this week. I feel it’s gone up a level from where we were in Jersey and we’re starting to see a better understanding of some of our tactics.
"There’s some new player combinations for us to have a look at this Saturday – which is good information for us as the Test Series approaches.
After a 28-10 win over Japan at Murrayfield last weekend, this Saturday’s match will be the first of five against South African club and provincial sides before there first test against the world champion Springboks.
These matches will serve as a chance for the the players to try and nail down a starting berth for that first test match on Saturday, July 24 with Welsh fly-half Dan Biggar having already impressed in the win over Japan.