An affidavit of marriage is a legal document and a sworn statement submitted to the court or another institution, to verify that two people are married. An affidavit is a legal document in which one or more parties affirm that a certain set of facts is true.An affidavit of marriage is a legally binding document that proves a legal marriage exists between two people. Affidavit: An affidavit is a sworn written statement that is the same as testifying under oath in court. PURSUANT TO VIRGINIA CODE SECTION 20-16. An affidavit is a written statement made under oath that is typically used in legal proceedings. Learn their purpose, when to use, and how to write. Resources and information to help you navigate your court case, including step-by-step guides for following procedures and help with understanding your options. This new Sixth Edition starts a second century for Black's Law. Dictionary-the standard authority for legal definitions since 1891.