Was just reading around this in Pascal recently.
Why is it the older I get, the more I like the French?
Wasn't he a Jansenist?
It's complicated. He wrote in defense of a friend who was a Jansenist in a series of infamous letters upbraiding and mocking the Jesuits of the time for their method of reasoning and conclusions drawn therefrom.
In light of the polemical and satirical tone of Pascal's writing, it is unclear what he believed and frankly I think such questions about any author are as irrelevant as they are undecidable.
Certainly he found some clear inspiration from the Jansenists in his social circle and family.
(IIRC) has no clear Jansenist slant.
In any case, I enjoyed revisiting his letters recently.