Erin,
I usually do look-ups in Catholic churches, but usually folk give me good info to shorten
the search time.
It seems you do not have a specific date or year for the marriage. And there were several Catholic churches in Newcastle at the time.
Some church records contain surname indexes which point to a specific page number, making the search easy. But some churches do not.
I will look in Tyne & Wear Archives to see if St Michael's has such an index.
Michael