It depends on whether the civil ceremony actually fulfills the substantive conditions of a nikah, not merely on which government office processed the paperwork. If a civil registration includes clear mutual consent, an identifiable offer and acceptance, a specified mahr, and witnesses — and there is no wali objection where one is required — many scholars would recognize it as a valid Islamic marriage even without a mosque ceremony, since Islam does not mandate a particular venue or officiant, only that the pillars be met. However, if a civil marriage is purely a legal registration with no wali involvement where required, no explicit mahr, and no religious intention behind the vows, a number of scholars consider it religiously incomplete, meaning the couple should still perform a proper nikah before living as husband and wife. Because Islamic marriage is described in the Quran as a solemn covenant, not a mere formality, couples are generally advised to ensure an explicit nikah — whether combined with civil registration or separate from it — rather than relying on secular paperwork alone to establish their religious status as spouses.
Q&A · Marriage & Divorce
Is a civil marriage without a separate Islamic contract considered valid?
References
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.