What does the Bible and God say about when a couple is considered married? Does there have to be a ceremony?

That's a tough question to answer since the marriage ceremony is very much cultural, legal, and religious.

The best information I could find was here www.answerbag.com/q_view/943357

The common thread I would gather from the majority of societies I've seen or studied is that there is always some public declaration before family and friends or the community that two people are being united. How this takes place varies greatly of course depending on the times, the religion, and the culture.

I can't find if the bible really says anything about eloping though.

But does there have to be a ceremony: yes.
Does it have to be like any ceremony you've seen before? No. All it really needs are friends, food, and loved one's coming to celebrate you uniting your life with a good and dear friend.

To answer your question Biblically you have to go back to the beginning. In Genesis 2:24 it talks about the two becoming one flesh (also see 1 Cor. 6:15-16), so it is when the marriage is consumated that God considers a couple married, of course the marriage has to be between two believers (2 Cor 6:14-15) in Christ.

Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh. And they were both naked, the man and his wife, and were not ashamed...Gen 2:24-25

Have ye not read, that he which made them at the beginning made them male and female,

And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?

Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.Matt 19:4-6

When you have Sex, you are no more Twain but one Flesh,...What therefore God hath joined together, let not man put asunder

When you have Sex God marrys you...

Lets Go back To Jacob...Laban did not Marry them..all he did is have a Feast..thats it...He did not say by the power invested in me I pernounce Husband and wife..all the had is a Feast

Jacob served seven years for Rachel; and they seemed unto him but a few days, for the love he had to her. 21 And Jacob said unto Laban, Give me my wife, for my days are fulfilled, that I may go in unto her. 22 And Laban gathered together all the men of the place, and made a feast.

Verse 23 Jacob went in to Leah...When Jacob came out he was a Married man

23 And it came to pass in the evening, that he took Leah his daughter, and brought her to him; and he went in unto her.
Gen 29:20-23

And she gave him Bilhah her handmaid to wife: and Jacob went in unto her.Gen 30:4

Another Example

John 2:2-And both Jesus was called, and his disciples, to the marriage. 3 And when they wanted wine, the mother of Jesus saith unto him, They have no wine.

Jesus was Invited to the Marriage feast , but Jesus did not Go in there

and , say , Your Married…Jesus did not do this

Jesus went there to do is turning water into wine

God Spoke the Word in the Beginning

Gen 2:24 - Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.25 And they were both naked, the man and his wife, and were not ashamed.

Have ye not read, that he which made them at the beginning made them male and female,

And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?

Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder. Matt 19:4-

You See? were is the Man that Marries you? Were is the Church they Got married in? Were is the Marriage License? God marries you not Man When you Leave your Father and your Mother and Cleave to your wife and you COME ONE with her YOUR MARRIED, God Joined you TOGATHER and it is till DEATH do you PART.

You are Bound by Gods LAW as Long as one or the Other is ALIVE Romans 7:2

The Word of God Tells us, What God Joined togather Let not Man Put asunder, So the Husband or the Wife divorces one or the Other Matt 19:9 Jesus says Even for the Cause of Fornication and shall marry another Commits Adultery, and who so Marries her that is Put away commits adultery,

So who ever Marries - they Break the 7th Commandment Because God joined you Togather, This is why it is Death do you Part, Even when People get married by there tradition ,they take a Vow Till Death do you Part

Romans 7:2 So then if, while her husband liveth, she be married to another man, she shall be called an adulteress: but if her husband be dead, she is free from that law; so that she is no adulteress, though she be married to another man.

Matt 19:6, Thy Shalt not Commit Adultery - Mark 10:19, Because the Partner is Alive, The Word of God Clearly Says if you break one Point of the Law, which is the Commandments, your Guilty of the Whole, Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law1 John 3:4

see James 2:10-11 , For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all. 11 For he that said, Do not commit adultery, said also, Do not kill. Now if thou commit no adultery, yet if thou kill, thou art become a transgressor of the law.