If you were married to a U.S. citizen who died before you were able to get permanent residence in the U.S. (a "green card") through the marriage, you quite possibly can get the green card anyway. This article will describe the qualification requirements and steps to take to successfully complete the process.
If your U.S. citizen spouse died before filing a petition on Form I-130 to start the green card process, you can potentially file a petition on your own. This way, you would let U.S. Citizenship and Immigration Services (USCIS) know that you were married to a U.S. citizen and that therefore you are eligible for a green card. (See I.N.A. Section 201(b)(2)(A)(i).) There are several requirements, however.
First, you and your deceased U.S. spouse must not have been divorced or legally separated at the time of the death. It's okay if you were living apart; the only thing that matters is that you weren't legally separated, that is, by court order. (A legal separation results when spouses separate and a court rules on the division of property, alimony, child support, custody, and visitation, but does not grant a divorce.)
Second, don't wait too long. You need to file the self-petition (called an "I-360, Petition for Amerasian, Widow(er), or Special Immigrant") within two years of the date your U.S. citizen spouse died.
Finally, it's best to file the self-petition before you get remarried, if that might be in your future. If you marry, you won't be able to self-petition on the basis of your marriage to the spouse who died. Of course, if you marry another U.S. citizen, you could have that person petition for you, but you might find it quicker, easier, and less expensive to file a self-petition before getting remarried. And if your new spouse is not a U.S. citizen, you will either have no chance at U.S. immigration or, if your spouse is a U.S. lawful permanent resident, possibly face delays.
If your spouse filed an I-130 petition for you but died before USCIS could rule on it, or if you had an application for adjustment of status (based on an approved I-130) pending (awaiting USCIS decision) at the time of your spouse's death, USCIS will still go through with your case. (See "Applying for Adjustment of Status as the Widow(er) of a U.S. Citizen.")
The same is true if you are overseas and intend to use consular processing to obtain an immigrant visa and green card.
The death of your U.S. citizen spouse doesn't excuse you from satisfying most other U.S. green card eligibility requirements, such as proving that the marriage was real (not a fraud) and that you are admissible to the United States. (See Legal Requirements for a Marriage-Based Visa or Green Card).
One admissibility problem some people face is too many days of "unlawful presence" in the United States. (See Consequences of Unlawful Presence in the U.S.--Three- and Ten-Year Time Bars.) If you were waiting on an I-130 petition approval when your spouse died, you don't acquire any (or any more) days of unlawful presence while you wait for USCIS to rule on your case.
You won't, however, need to worry about inadmissibility based on not having a financial sponsor file a Form I-864 Affidavit of Support on your behalf. Widow(er)s of U.S. citizens are exempt from this requirement, and should indicate this in their application by filing an I-864W.
If you are outside the U.S. because you were deported, but your deceased U.S. citizen spouse had filed an I-130 petition that is still pending, you can potentially apply for an immigrant visa (green card) from outside the country. USCIS will let you reapply if:
Nevertheless, you'd definitely want to seek a lawyer's help with this complex sort of request.
U.S. immigration law is complicated under the best of circumstances, and the death of a U.S. citizen spouse adds another layer; not to mention that it creates a trying time emotionally. Under such circumstances, getting an attorney's help can make your life easier and increase the chances that your U.S. residence application will gain approval.