If you want to bring a fiancé(e) into the U.S. on a K-1 visa to get married and apply for a green card, and your fiance has a criminal record, that fact is likely to trigger inadmissibility. In other words, your fiance would be ineligible for the visa or to enter the United States. This can hold true for crimes committed even without a formal conviction or arrest. However, depending on the crime, it may still be possible to bring your loved one into the country by requesting a waiver of inadmissibility.
A waiver of inadmissibility essentially asks the U.S. government to overlook your fiance's criminal record so that the person can receive a visa to enter the United States (or receive some other immigration benefit).
Although the K-1 is technically a nonimmigrant visa, under which circumstances a person would normally request a nonimmigrant waiver, the fiancé visa is treated a little differently. After all, your fiancé very likely intends to remain in the U.S. permanently, by filing for adjustment of status (a green card) after the marriage. Therefore, the fiancé would need to request an immigrant waiver by filing USCIS Form I-601, Application for Waiver of Grounds of Inadmissibility.
Because of the strict immigration laws in the U.S., even the most non-serious of illegal activity can trigger inadmissibility. In fact, the immigration laws do not even allow a waiver for the following crimes:
To learn more about the different categories of crimes that will trigger inadmissibility see What Crimes Make Immigrants Inadmissible to the U.S.?
If you not sure whether your fiance will qualify for a waiver, you have two options:
Even if a waiver is available, your fiancé will still have to convince the government that he or she deserves it. Each application is decided based on the particular circumstances of the situation. Applicants must meet strict criteria, and decisions are made on a case-by-case basis. For a fiancé to qualify, he or she must demonstrate that a "qualifying relative" (in this case, the intended U.S. citizen spouse) will face extreme hardship if the waiver is not granted.
General hardships, such as financial issues, are to be expected if someone's fiance is denied a U.S. visa. Therefore, such hardships alone are not usually sufficient to meet the extreme standard. And only hardship to the U.S. citizen fiancé (e) is taken into account.
Meanwhile, all negative factors relating to the foreign national will be considered and weighed against the favorable hardship factors, such as:
In a nutshell, while the U.S. government wants to protect the U.S. citizen from hardship that is extreme, it must also safeguard society as a whole. You can learn more about what factors constitute extreme hardship in the article, Showing Extreme Hardship for the I-601 Waiver Process.
It is not possible to predict the outcome of a case without an in-depth analysis of the facts surrounding the situation. The chances of a denial are high, so you are strongly urged to consult with an experienced immigration attorney to discuss your situation before filing an application for a fiance visa.