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.
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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.
Schmidt was also able to make up for the loss of injured flanker Josh van der Flier's off the bench with the recovered Peter O'Mahony, while lock Iain Henderson and winger Andrew Trimble are also back among an impactful bunch of replacements.
"We're really hopeful that they are primed to contribute, because I think the French replacements are really strong as well. The last 30 minutes of the match is going to be very, very high contested," Schmidt said.
"I think they (France) are really dangerous. They certainly appear to have the right mix and the right players. I know talking to (France manager) Guy (Noves) last year, they were putting foundations in that to me sounded quite promising, and hopefully they don't come to fruition on Saturday."
Ireland and France have so far won one game and lost the other, meaning the loser on Saturday would likely be out of contention, with leaders England expected to make it three wins from three against bottom-placed Italy on Sunday.
Ireland team: 15-Rob Kearney, 14-Keith Earls, 13-Robbie Henshaw, 12-Garry Ringrose, 11-Simon Zebo, 10-Johnny Sexton, 9-Conor Murray; 8-Jamie Heaslip, 7-Sean O'Brien, 6-CJ Stander, 5-Devin Toner, 4-Donnacha Ryan, 3-Tadhg Furlong, 2-Rory Best (captain), 1-Jack McGrath
Replacements: 16-Niall Scannell, 17-Cian Healy, 18-John Ryan, 19-Iain Henderson, 20-Peter O'Mahony, 21-Kieran Marmion, 22-Paddy Jackson, 23-Andrew Trimble
(Editing by Hugh Lawson)
