There is a lot of information about how people will marry so that a non-U.S. citizen spouse can get a green card to legally live in the country. However, for those looking to make the U.S. a permanent home, the focus should be on marrying a citizen to get citizenship.
The USCIS explains that marrying a U.S. citizen does not grant immediate citizenship to anyone. A person will still have to go through a process to qualify for naturalization. This requires meeting specific requirements that anyone who wants to become a citizen must meet along with meeting special requirements as the spouse of a citizen.
You may apply for naturalization if you have been living with and married to your spouse who is a U.S. citizen for at least three years. During that time, you also need to have held a green card. There are also general requirements you must meet. If you fail to meet requirements, the U.S. can refuse your naturalization request despite your marriage, so keep that in mind and make sure you meet all requirements before you submit your application.
You must have a permanent residence within the state where you want to file for citizenship for at least three months. You need to have been in the U.S. for at least 18 months in the previous three years, but you must have an established residence for the whole three years, and you cannot live outside the U.S. once you file your application. You must meet good moral character standards, be at least 18 years old and be fluent in English.
Your spouse must also be a U.S. citizen for your entire marriage, which must be three years before you apply for naturalization. You also need to show that you will obey the laws of the U.S. and be a productive citizen should you gain citizenship.