Answer: This is a difficult question to answer because the Bible nowhere explicitly states at what point God considers a couple to be married. There are three common viewpoints: 1) God only considers a couple married when they are legally married. 2) A couple is married in God’s eyes when they have completed some kind of formal wedding ceremony. 3) God considers a couple to be married at the moment the marriage is consummated with sexual intercourse. Let’s look at each of the three views and see what strengths and weaknesses each has.
1) God only considers a couple married when they are legally married. The scriptural support typically given to this view is the verses that advocate submission to the government (Romans 13:1-7; 1 Peter 2:17). The argument is that if the government requires certain “paperwork” to be completed before a marriage is recognized, a couple should submit themselves to whatever process the government requires. It is definitely biblical for a couple to submit to the government as long as the requirements do not contradict God’s Word and are reasonable. Romans 13:1-2 tells us, “Everyone must submit himself to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. Consequently, he who rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves.”
There are some weaknesses and potential problems with this view. First, there were marriages before any government was organized. For thousands of years, people were getting married with no such thing as a marriage license. Second, even today, there are some countries that have no governmental recognition of marriage, and/or no legal requirements for marriage. Third, there are some governments that place unbiblical requirements on a marriage before it is legally recognized. As an example, there are countries that require a wedding to be held in a Catholic church, according to Catholic teachings, and overseen by a Catholic priest. Obviously, for those who have strong disagreements with the Catholic Church and the Catholic understanding of marriage as a sacrament, it would be unbiblical to submit to being married in the Catholic Church.
2) A couple is married in God’s eyes when they have completed some kind of formal wedding ceremony. Similar to the way—in many cultures—a father gives away his daughter at the wedding, some interpreters understand God’s bringing Eve to Adam (Genesis 2:22) as God’s overseeing the first wedding “ceremony.” In John chapter 2, Jesus attended a wedding ceremony. Jesus would not have attended such an event if He did not approve of what was occurring. Jesus’ attending a wedding ceremony by no means indicates that God requires a wedding ceremony, but it most definitely does indicate that a wedding ceremony is acceptable in God’s sight. Nearly every culture in the history of humanity has had some kind of formal wedding ceremony. In every culture there is an event, action, covenant, or proclamation that is recognized as declaring a man and woman to be married.
3) God considers a couple to be married at the moment the marriage is consummated with sexual intercourse. There are some who argue that if any man and woman have sex, God considers the two of them to be married. Such a viewpoint is not biblically sound. The basis for this argument is the fact that sexual intercourse between a husband and wife is the ultimate fulfillment of the “one flesh” principle (Genesis 2:24; Matthew 19:5; Ephesians 5:31). In this sense, sexual intercourse is the final “seal” on a marriage covenant. However, if a couple is legally and ceremonially married, but for some reason is unable to engage in sexual intercourse, the couple is still considered married.
It is not biblical to consider a couple who have had sexual intercourse—but who have not observed any of the other aspects of a marriage covenant—to be married. Scriptures such as 1 Corinthians 7:2 indicate that sex before marriage is immorality. If sexual intercourse causes a couple to become married, it could not be considered immoral, as the couple would be considered married the moment they engaged in sexual intercourse. There is absolutely no biblical basis for an unmarried couple to have sex and then declare themselves to be married, thereby declaring all future sexual relations to be moral and God-honoring.
So, what constitutes marriage in God’s eyes? It would seem that the following principles should be followed: 1) As long as the requirements are reasonable and not against the Bible, a couple should seek whatever formal governmental recognition is available. 2) A couple should follow whatever cultural and familial practices are typically employed to recognize a couple as “officially married.” 3) If possible, a couple should consummate the marriage sexually, fulfilling the physical aspect of the “one flesh” principle.
What if one or more of these principles are not fulfilled? Is such a couple still considered married in God’s eyes? Ultimately, that is between the couple and God. God knows our hearts (1 John 3:20). God knows the difference between a true marriage covenant and an attempt to justify sexual immorality.
(Source of info: gotquestions.org)