What is the religious ruling on a Muslim man marrying a Christian woman in a church, knowing that the engagement was conducted according to Islamic Sharia?

It is not permissible for a Muslim man to marry a non-Muslim woman unless she is a chaste woman of the People of the Book. This marriage has its pillars and conditions, among them that the guardian of the woman of the People of the Book must be from her own religion, and that the two witnesses must be Muslim according to the majority of jurists. If a condition is violated, such as the absence of a guardian or Muslim witnesses, the marriage is invalid. If no contract was concluded at all, then she remains a stranger (non-mahram (definition)).

As for the condition of completing the wedding ceremony according to the Christian religion in a church, this is not permissible, due to the veneration of the church involved. A church often contains objectionable matters, polytheistic or false rituals, and music. Going there involves mingling with and acknowledging people who commit objectionable acts. Despite the permissibility of marrying a chaste woman of the People of the Book, it is still disliked due to the potential prohibitions that may arise from it.