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. To make a marriage license valid it must have signatures from the individuals looking to get married, two witnesses, and the person who preformed the ceremony.Two individuals seeking to become domestic partners must complete and file a declaration of domestic partnership in person with the City Clerk Department. The. 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. You are required to complete an Affidavit of Financial Information.