The Islamic ruling with regard to marrying Christian and Jewish women does not differentiate between cases of taking a second wife and other cases. The ruling is the same. In this regard we would like to quote sheikh Yusuf Al-Qaradawi who said,
Islam has made marriage to Jewish or Christian women lawful for Muslim men, for they are Ahl al-Kitab, that is, People of the Book, or people whose tradition is based upon a divinely revealed Scripture. Although they have distorted and altered it, they do possess a religion of divine origin, and hence Islam has made some exceptions in dealing with them. The Qur’an says: “…And the food of those who were given the Scripture (before you) is permitted to you and your food is permitted to them. And (lawful to you in marriage are) chaste women from the Believers and chaste women from those who were given the Scripture before you, when you give them their due cowers, desiring chastity, not lewdness or secret intrigues…” (Al-Ma’idah 5:6)
Tolerance of such a degree is a characteristic of Islam which is hardly to be found among other faiths and nations. Despite the fact that Islam takes the People of the Book to task for their unbelief and error, it permits the Muslim to marry a Christian or Jewish woman who may, as his consort, the mistress of his house, the mother of his children, the source of his repose, and his companion for life, retain her own faith—all this, while the Qur’an says concerning marriage and its mystique: “And among His signs is that He created for you mates from among yourselves, that you may dwell with them in tranquility, and He has put love and mercy between you…” (Ar-Rum 30:21)
However, a warning is in order here. In order of preference, a believing, practicing Muslim woman who loves her religion is preferable to a nominal Muslim woman who has inherited Islam from her parents. The Prophet (peace and blessings be upon him) said, “Get the one who is religious and prosper.” (Reported by al-Bukhari)
It is also obvious that a Muslim woman, regardless of who she is, is better suited to a Muslim man than a woman of Christian or Jewish faith, regardless of her merits. If a Muslim man has the slightest suspicion that a non-Muslim wife might affect the beliefs and attitudes of his children, it becomes obligatory on him to exercise caution.
If the number of Muslims in a country is small—for example, if they are immigrants residing in a non-Muslim country—their men ought to be prohibited from marrying non-Muslim women because, since Muslim women are prohibited from marrying non-Muslim men, their marriage to non-Muslim women means that many Muslim girls will remain unmarried. Since this situation is injurious to the Muslim society, this injury can be avoided by temporarily suspending this permission.
The first wife’s knowledge of the second marriage does not affect its validity. In fact her consent is not a condition, though it is a kind of good manners and kindness to seek her approval. In case the first wife has stipulated in the marriage contract that the husband must not take another wife besides her, she has the right to seek divorce if she doesn’t accept and cannot live with the second marriage.