Barnes, who missed the 40-8 thrashing of the Bulls in Brisbane, has recovered from a calf injury and will replace Charlie Fetoai, with Reds coach Phil Mooney sticking with Quade Cooper at number 10.
Speaking from the team's training base in Pretoria, Mooney said: "Berrick is an international player and we need him in the side. It is tough on Charlie as he did an excellent job for us when called into the side against the Bulls.
"It is fantastic for our depth to have a player like him who can step up at short notice and perform so well."
Mooney confirmed the selectors had otherwise kept faith with the impressive outfit which pulled off the stunning win over the defending champions.
He said: "The 22 did the job against the Bulls. It's now up to them to give us a back-to-back performance of the same or better quality against the Lions."
The Lions are 12th in the competition table, five points behind the Reds.