Q: Are non-Catholic marriages valid?
A: Well, not all of them, of course. Just like there are Catholics who try to marry under invalidating impediments or who choose not to give valid matrimonial consent, so there are non-Catholics do so.
However, merely because a marriage is between two non-Catholics does not mean it is invalid. If two baptized non-Catholics marry each other then they can have a valid sacramental marriage. This is because a priest is not necessary to perform the sacrament of matrimony. It is formed by the two partners, who create the sacrament between them by giving valid matrimonial consent to the other and then consummating the union. In Catholic churches the priest serves as the Church’s witness and overseer of the event, but he is not necessary for the sacrament itself to be performed.
In the same way, two unbaptized people (or one baptized and one unbaptized) can have a valid natural (non-sacramental) marriage between them even though the Church is not involved.
The Church exercises its pastoral responsibility toward its members by requiring them to get the ecclesiastical equivalent of a wedding license before marrying, just as the state requires its citizens to get one. However, this requirement is not applicable to those who are not citizens of the Church. If their churches or religious institutions (foolishly) do not play a pastoral role by requiring their members to go through marriage preparation and approval to help secure the viability of the marriage then that is their business.
Not long ago I received a letter from a husband and wife pair of anti-Catholic Baptist missionaries to Italy who had read my conversion story. I had mentioned in it that my original marriage ceremony to my dear, late wife Renee had been invalid because she was a Catholic and we married outside the Church without a dispensation, and this led them to challenge me by attacking an imaginary teaching that non-Catholic weddings are invalid.
I was flabbergasted by the lack of understanding of Catholic theology they displayed for a couple who considered themselves knowledgeable enough to go to Italy as anti-Catholic missionaries. The reason our original marriage ceremony was invalid was that Renee was a citizen of the Church, yet failed to get a dispensation to marry me in a non-Catholic ceremony (or marry me for all for that matter) — a fault which we later corrected.
Yet in their arrogant ignorance of Catholic belief they inferred that Catholics teach that all marriages outside the Church are invalid and were confident enough to shoot their mouths off about it to a Catholic before checking it out. Unfortunately, this level of ignorance (and arrogance) is typical of professional anti-Catholics, including very well known ones.