Use this form to show they have adequate means of financial support and are not likely to rely on the US government for financial support. This affidavit is a contract between a sponsor and the U.S. Government.Completing and signing Form I-864 makes you the sponsor. If you are filing Form I864 as the petitioning sponsor, use our How to Fill Out Affidavit of Support Form I864 guide. In this guide, we will explain who needs to complete Form I864, when to file it, and how to fill out Form I864 stepbystep. Fill in the sponsor's full name, date of birth, and contact information. Specify the relationship to the immigrant. Stepbystep instructions on filling out Form I864, Affidavit of Support. The person who signs the Affidavit of Support is also called the "sponsor. Form I864, Affidavit of Support, needs to be filed DHS if you are a U.S. citizen or LPR planning to sponsor a spouse or family member.