What is the ruling of Islamic law regarding a woman who marries while still legally married to another man? Is she required to observe a waiting period after divorce from the second marriage?

If the second husband entered into marriage with this woman while knowing that she was still in a valid marriage with another man, then the second marriage is void (batil), and she is not required to observe a waiting period (‘idda) even if the marriage was consummated. This is because the marriage is void and amounts to adultery, which is not accorded any sanctity in Islamic law.

However, if the second husband entered into the marriage while unaware of her existing marriage, then the second marriage is defective (fasid) and must be dissolved under Islamic law. In such a case, the woman must observe a waiting period if the marriage was consummated, in order to protect the husband’s right to establish paternity of his child, given his ignorance of her prior marriage.

And Allah Almighty knows best.