In Islam, the marriage of a man and a woman is not just a financial and physical arrangement of living together, but a sacred contract, a gift of Allah, to lead a happy, enjoyable life and continue the lineage.
The main goal of marriage in Islam is the realization of tranquility and compassion between the spouses. Being a solemn contract, the sharia lays down rules and arrangements for marriage to guarantee its stability.
As regards the Sunni-Shiite Marriage, we’d like to cite the following fatwa issued by the eminent Muslim scholar, Sheikh Yusuf Al-Qaradawi:
“Matrimonial life should be based on mutual understanding between the spouses rather than spent in heated arguments and continuous debates. Life should not be a battle between the spouses: one of them supports Abu Bakr and the other defends `Ali. I don’t say this kind of marriage is haram, but I do not prefer it. There should be a kind of harmony between the spouses, and this is not found if the Shiite is fanatic. One of them would say, “may Allah be pleased with Abu Bakr” and the other would say, “May Allah’s curse be inflicted on him”. This is not a good example of matrimonial life.
I am not totally against this marriage, because I permit the Muslim to get married to a Christian lady, and if it is allowed for a Muslim to marry a Christian lady, then, in fortiori, it is allowed to marry a Shiite lady.
Still, though marriage is valid in principle, it is not the ideal one.
Therefore, I suggest – if a Muslim really wants to get married to a Shiite lady – to marry a moderate Shi`ite woman who prays in the Masjid with Sunnis and attends the Khutbah and doesn’t support conflict with the Sunnis. If she is as such, then it is permissible to get married to her.”
It goes without saying that the above fatwa is also applicable in case the man is a Shiite and the woman is a Sunni.