An affidavit of marriage is a legally binding document that proves a legal marriage exists between two people. 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. An Affidavit is simply a written, notarized sworn statement. An affidavit is a sworn statement of fact that can be used in a variety of legal proceedings, from bankruptcy cases to family and civil litigation matters. You need to provide identification and possibly proof of age. Arizona does not require a blood test or a copy of your dissolution of marriage decree. An Affidavit of Eligibility to Marry. Some countries need this as proof of legal ability to enter into a marriage contract. And at the Clerk of the Superior Court office at the courthouse, which is located at 1316 Kofa.