My brother-in-law got married to a non-catholic. They were married by his wife’s Minister/Pastor. If he chose to have his marriage blessed in the Catholic Church, would he be able to since he was married by another religious, non-catholic, person? If so, what would he have to do in order to have his marriage blessed in the Catholic Church?
Assuming your brother is Catholic, and that he was married without a dispensation from form (permission to hold a non-Catholic form of ceremony) from his bishop, he will need to see his parish priest to inquire about having his marriage convalidated - this is sometimes called “having the marriage blessed” (usually by those who have not needed to have their marriage convalidated

).
From memory, there are generally two types of convalidation: (i) a renewal of consent (basically a new ceremony, small and private or as big and public as the couple wants), and (ii) radical sanation (which I believe translates as “cleansing from the root”), which usually involves the Catholic party petitioning his bishop, through his pastor and diocesan marriage tribunal, for what is in effect an after-the-fact dispensation from form for the original non-Catholic ceremony. The latter is the route I took (my non-Catholic wife was distrustful of Catholic church authority and “the nerve” of the Church to tell her our marriage was not valid - not that anyone blames her, it is a tough teaching), and our marriage was convalidated via radical sanation last summer. I immediately went to confession and was then back in the bosom of Mother Church.
For more info, I suggest doing a search on the terms “convalidation” and “radical sanation” - you’ll get much better information than my summarized version.
As posted above, marriage preparation may be needed, depending on the specific circumstances.
We will be praying for your brother-in-law, and his espoused.
Peace all.