A US Citizen, who plans to get married in the US to his/her foreign fiancé is eligible to file a K-1 petition with the USCIS on behalf of his/her fiancé. Once the petition is approved, the fiancé will be able to obtain a visa issued at a U.S. consulate abroad. When the fiancé comes legally to the US, the marriage must take place within 90 days of the fiancé entering the United States.
If the marriage does not take place within 90 days, the fiancé will be required to leave the United States, even if s/he marries someone other than the petitioner. A fiancé may not obtain an extension of the 90-day original nonimmigrant admission. If the fiancé leaves the country before the marriages takes place, the fiancé must obtain a new visa to be allowed back into the United States.
Once the marriage takes place, the fiancé (now the spouse) will be eligible to apply for a permanent resident status at the local USCIS.