Williams made his Wales debut in June last year and has six caps, compared to 36 for Davies, who has only recently returned from a thigh injury and will be among the replacements.
Gatland opted instead to pair Williams with his Blues team mate Gareth Anscombe, who will start in the flyhalf berth at the Stade de France.
"Gareth didn't train all week so the call was made on fitness as much as anything," Gatland told reporters.
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"It's a good opportunity for him (Williams). He's not the biggest but he’s competitive. He has things to work on but he’s one for the future.
"He has some x-factor. It’s a position of depth at the moment with Gareth and Aled Davies but we’re still looking for some improvement."
Ken Owens is set to make a 61st appearance that would make him the most capped hooker in Welsh history.
Josh Navidi is back from injury to start at flank in a back-row that also includes Justin Tipuric and number eight Ross Moriarty.
Alun Wyn-Jones will captain the side from lock in what is his 49th Six Nations appearance.
Hadleigh Parkes and Jonathan Davies continue their partnership at centre with Josh Adams, George North and Liam Williams making up the back three.
Leigh Halfpenny, Leon Brown, Rhys Patchell and Scott Williams were not considered due to injury.
"I haven’t really contemplated anything other than winning the Six Nations. I don’t think about a (finishing) position," Gatland says.
"We came second last year which was okay but you want to win. I think if we win the first game, we can win the Six Nations."
Wales are on a nine-match unbeaten run in what is Gatland's final season with the side before he ends his 12-year tenure after the World Cup in Japan.
Team: 15-Liam Williams, 14-George North, 13-Jonathan Davies, 12-Hadleigh Parkes, 11-Josh Adams, 10-Gareth Anscombe, 9-Tomos Williams, 8-Ross Moriarty, 7-Justin Tipuric, 6-Josh Navidi, 5-Alun Wyn Jones (captain), 4-Adam Beard, 3-Tomas Francis, 2-Ken Owens, 1-Rob Evans
Replacements: 16-Elliot Dee, 17-Wyn Jones, 18-Samson Lee, 19-Cory Hill, 20-Aaron Wainwright, 21-Gareth Davies, 22-Dan Biggar, 23-Owen Watkin
(Reporting by Nick Said; editing by Ken Ferris)
