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.This video will help you to fill out I-864 For Joint Sponsor. If you are filing Form I864 as the petitioning sponsor, use our How to Fill Out Affidavit of Support Form I864 guide. You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. Line-by-line guidance for properly filling out USCIS's I-864 Affidavit of Support to sponsor an immigrating family member. In this guide, we will explain who needs to complete Form I864, when to file it, and how to fill out Form I864 stepbystep. Stepbystep instructions on filling out Form I864, Affidavit of Support. Form I-864 is required for most family-based immigrants and some employment-based immigrants to show that they have adequate means of financial support. The petitioning sponsor must complete and submit a signed Form I864 for the intending immigrant even if a joint sponsor participates.