Sexton, who has suffered a spate of injuries recently from numerous concussions to shoulder, hamstring and neck problems, missed Ireland's first two matches of the tournament with a calf injury, when he was ably replaced by Paddy Jackson.
Despite only playing two of Ireland's last nine matches and just three times for his province Leinster since October - failing to play more than 60 minutes on each occasion - the 31-year-old's experience will be vital, Schmidt said.
"He was frustrated missing those first two and he's excited by the opportunity, and he takes a fair bit of responsibility as well. He's obviously a leader within the team, and his experience contributes some of that leadership," Schmidt told a news conference on Thursday.
The New Zealander made two other changes after the 63-10 rout of Italy last time out, both in the front row. Prop Jack McGrath starts ahead of Cian Healy, and captain Rory Best returns after missing out on a 52nd consecutive Six Nations match through a last-minute illness in Rome.