The full-back, who also has experience of playing on the wing, comes in after recovering from an ankle injury.
That setback had kept Amos out of Pivac's initial plans, but he could now step up to play an important role over the remaining three matches.
The 25-year-old former Dragons star is looking to add to his 22 caps for Wales and takes the place of Cardiff Blues team-mate Owen Lane, who dropped out after suffering a hamstring blow.
Amos proved his fitness in Cardiff's Pro14 match against Connacht on Saturday, playing on the left wing in the Blues' 29-0 defeat.
Wales will look to return to winning ways after their 24-14 defeat to Ireland last time out, but in France they face a side who have started their campaign with purpose.
Les Bleus will be chasing a third successive victory, having already overcome England and Italy at the Stade de France.
A first away match for France promises to be their biggest test yet, with Wales having won their last three encounters, including a 20-19 success in their World Cup quarter-final in October.