The K-1 visa is a nonimmigrant visa for foreign fiancés of U.S. citizens, allowing them to enter the U.S. to get married within 90 days. A marriage-based green card is an immigrant visa given after marriage to a U.S. citizen or lawful permanent resident, allowing the foreign spouse to live permanently in the U.S.

Only U.S. citizens can file for a K-1 fiancé visa, whereas both U.S. citizens and green card holders can sponsor a spouse for a marriage-based green card. However, green card holders cannot bring a fiancé on a K-1 visa they must marry first.

To apply for a K-1 visa, the couple must be legally engaged and must have met in person within the last two years, unless certain exceptions apply. On the other hand, a marriage-based green card requires that the couple is already legally married before starting the application process.