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. Completing and signing Form I-864 makes you the sponsor.You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864. 30 The joint sponsor must sign a separate Affidavit of Support, Form I-864. In today's video we are going to be filling out form i 864 the affidavit of support form for the joint sponsor. The affidavit of support is a contract between the sponsor and the federal government. If you are filing Form I864 as the petitioning sponsor, use our How to Fill Out Affidavit of Support Form I864 guide. When applying for a green card through family sponsorship, one of the essential steps is completing the Affidavit of Support (Form I864). A fully completed and signed Affidavit of Support (Form I864) from the sponsor.