A Muslim woman is absolutely prohibited to get married to a non-Muslim man whether he is an atheist, disbeliever, Jew or a Christian.

This has been explicitly mentioned in the Qur’an, “And do not marry polytheistic women until they believe. And a believing slave woman is better than a polytheist, even though she might please you. And do not marry polytheistic men [to your women] until they believe. And a believing slave is better than a polytheist, even though he might please you. Those invite [you] to the Fire, but Allah invites to Paradise and to forgiveness, by His permission. And He makes clear His verses to the people that perhaps they may remember.” (Al-Baqarah 2:221)

An exception for this rule has been given to a Muslim man to marry a Christian. This is mentioned in the Qur’an, “And [lawful in marriage are] chaste women from among the believers and chaste women from among those who were given the Scripture before you, when you have given them their due compensation, desiring chastity.” (An-Nisaa’ 4:5)

In case a woman marries a non-Muslim man, this marriage is null and void even if it is conducted by having witnesses because ‘witnesses’ are not the only condition for a valid marriage in Islam. Such a relationship is prohibited and is classified as adultery or fornication.

May Allah guide you to the straight path.

Allah Almighty knows best.