From a reader…
Can a male catholic who has not been ordained to the priesthood become Pope?
The prerequisites are that he be
1) male, because he must become Bishop of Rome, and it is impossible for females to be given or for them to receive the Sacrament of Orders.
2) sui compos, because he must understand the question he is asked at his election and then express his consent.
Most authors think that he has to be baptized, though it seems possible that he has to at least be willing to be baptized (otherwise he could not also be ordained). Also, some author think that he cannot be a manifest heretic or schismatic, which seems reasonable, but not all writers think that’s a deal-breaker.
He doesn’t have to be smart or, it seems, wise, holy, kind, any of those things which we would prefer.
It has been hundreds of years since a non-Cardinal was elected. However, when and if such a thing would happen, were the man who was elected (probably brought into the conclave) to assent, he would have to be ordained immediately. The election of a non-bishop would be valid, but he wouldn’t be Roman Pontiff in the full sense until the moment he became a bishop.