Answer
(Fatwa: 608/464/D=1431)
Marrying non-Muslim girl is not lawful. Presently the ahl kitab (people of the book) have usually turned atheist and freethinker. And those who are ahl kitab merely by name, there are too many evils in marrying their daughters. Hence Hadhrat Umar Farooq (رضي الله عنه) forbade people from it in his age. So a Muslim should marry only Muslim girls. It is mentioned in the holy Quran:
وَلأَمَةٌ مُّؤْمِنَةٌ خَيْرٌ مِّن مُّشْرِكَةٍ وَلَوْ أَعْجَبَتْكُمْ [البقرة : 221].
Thus, doing nikah with atheist and freethinker ahl kitab is not lawful.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband