What is the moral status of common-law marriage?

Basically I agree with Caleb, but let me add a few comments too long to fit in a comment.

To the best of my knowledge, nowhere does the Bible specify any particular ritual or vows about marriage. Is it even necessary to say: Failing to follow human marriage customs does not make you any less married. Like, if you had a wedding with no bridesmaids or if you had "wedding donuts" instead of "wedding cake", I think few people would suppose this makes your marriage invalid. If you fail to update your relationship status on Facebook to "married", this does not make you any less married. Etc.

The question, then, is just how God defines "marriage". I don't know of any single Bible verse that says, "Thus spake the Lord, to be married in My sight thou must ..." But the Bible does make a number of statements about the nature of marriage that give strong clues. Like Gen 2:24, "Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh." Matt 19:6, "Therefore what God has joined together, let not man separate." And 19:9, "And I say to you, whoever divorces his wife, except for sexual immorality, and marries another, commits adultery; and whoever marries her who is divorced commits adultery." 1 Cor 7:3-4, "Let the husband render to his wife the affection due her, and likewise also the wife to her husband. The wife does not have authority over her own body, but the husband does. And likewise the husband does not have authority over his own body, but the wife does." Etc. You can pick up numerous other statements here and there.

So putting a little interpretation on this, I conclude that basically, in God's eyes, a marriage is a commitment between a man and a woman that for as long as they are both still alive they will live together, and limit their sexual activity to each other and not deny each other. Maybe you'd add something in there about raising children or other points I'm skimming over, but I think that's the bare essentials.

In my humble opinion then, if a man and a woman make such a commitment to each other, even if they do it sitting on the porch with no one else around, then they are married. If later one of them has sexual relations with someone else, that makes it adultery.

We could certainly debate how serious their intentions must be and whether they need to consummate the marriage. I presume that's part of why societies have built up rituals. If it was accepted that all it took to get married was for one person to say, "Hey, you want to get married?" and the other to say "okay", there would surely be many confused situations where one person thought they were getting married and the other didn't, like one person meant "right now" and the other meant "someday". But if you both go through an elaborate ritual and recite vows, there's surely no question of your intent. But on the flip side, if two people are in a plane crash and stranded on an uninhabited island and they decide they want to get married, the fact that there is no minister around to perform the wedding, no government agency to issue the license, no place to buy a wedding gown, etc etc, would be largely irrelevant.

If the government requires married couples to register in some way, than presumably Christians should comply with that in accordance with the general principle of obeying civil authorities. But getting a government-issued marriage license isn't what makes you married, any more than getting a government-issued birth certificate is what makes you be born.

Obviously a common law marriage is not a sacramental marriage. But, as it is part of the social compact in some places, someone who is common law married has the same moral standing. If you attempted some form of bigamy with a Catholic, the priest would ask you in accord with:

Can. 1085 §1. A person bound by the bond of a prior marriage, even if it was not consummated, invalidly attempts marriage.

"Are you currently married" and you would say, yes.

Similarly, there is no impediment for cohabitating couples to have their marriage sacramentalized by the Catholic Church (except a good long confession by both parties and maybe some other penances as prescribed by the priest).

But, if a common law married man abandons his common law wife to marry another woman, he must get a divorce from her before trying to get a sacramental marriage through the Church.

One thing to keep in mind is the assumption of the automatic nature of common law marriage might not be what you think it is. I was told the same thing you described, but in researching a bit, I think a couple still needs to make a formal declaration, so the marriage isn't just something that falls in your lap.

Allowances of the law have little or no bearing on the moral standing of marriage or any other Christian practice. Where applicable we are bound to follow relevant laws in addition to the prescription of our doctrine, but this is in addition to not in place of them. Common law does not define marriage, although it may or may not make an applicable legal hoop necessary.

Most of marriage practice among Christians boils down to tradition, but the traditions are built on principles. While much variation is found in the details, the principles guiding what is or is not done are pretty fixed. Marriage is a covenant relationship between one man and one woman entered into by profession before men and sealed by God.

How you go about that, the pieces have to all be there. Where the profession is made -- in church or on a lawn, whether officiated by an uncle or pastor or even not at all -- doesn't matter nearly so much that a declaration is made public that two people are now married. Where they sign state paperwork before our after our not at all if not required doesn't change anything. Making such a declaration, then sleeping with someone else would be a violation of that covenant no matter where the state stands.

Christianity even honors marriage as sacred when entered into by two non Christians with a purely secular profession. God's role in the covenant relationship is something we believe just is -- even if the parties involved ignore him.

Obeying the law of the land is required, but our duties do not end where the law stops.