New convert’s marriage before embracing Islam is still valid, and they do not need to have a new marriage contract after they have been guided to Islam. In other words, the marriage of non-Muslim people is not nullified by their embracing of Islam. But if they wish to reinstate their marriage contract again after they embraced Islam, they may take the Imam of the local mosque as their wali, so long as their relatives are non-Muslims.
Also, it should be known that Imam Abu Hanifah (may Allah have mercy on him) maintained that an adult, rational woman is capable of contracting her own marriage without a wali. Therefore, the marriage is undoubtedly legal.
In this regard, we’d like to cite the following by the eminent Muslim scholar, Dr. Abdul-Rahman Muhammed Yaki: “Islamically, if two couples get together as man and woman and before they accepted Islam they are living as man and wife, as soon as they accept Islam their marriage is valid; they don’t need to re-marry Islamically. On that note, we would regard the marriage that is being done according to culture or any system before they accept Islam as valid marriage. As soon as they accept Islam they will go on with their life as usual, as man and wife.