First, let's get one important thing straight: Marriage to a U.S. citizen makes someone eligible for U.S. lawful permanent residence (a "green card"), not for U.S. citizenship. (At least, not in the short term.) Having a green card for a certain number of years can make the person eligible for U.S. citizenship.
Get married to a US citizen. File form I-130 with the USCIS. File form I-485 if you are currently in the United States or form DS-260 if you are living outside of the U.S.
3 Years of Continuous Residence. The spouse of a U.S. citizen residing in the United States must have continuously resided in the United States as an LPR for at least 3 years immediately preceding the date of the filing the application and up to the time of the Oath of Allegiance.
Naturalization Process for Marriage Green Card Holders Meet Eligibility Requirements. Prepare Form N-400. Biometrics Appointment. Naturalization Interview. English and Civics Tests. Oath of Allegiance Ceremony. Receive Certificate of Naturalization.
You may file Form N-400, Application for Naturalization, 90 calendar days before you complete your continuous residence requirement if your eligibility for naturalization is based upon being a: Permanent resident for at least 5 years; or. Permanent resident for at least 3 years if you are married to a US citizen.
No, marriage to an American citizen does not confer automatic citizenship or immigration status. Marriage to an American citizen lets that citizen petition their government to allow their spouse to immigrate, ie to apply for permanent residency (``green card'').
Your US citizen spouse would complete form I-130, Petition for Alien Relative. You would complete form I-485, Application to Adjust Status and Register Lawful Permanent Residence. Both of these forms require supporting forms and evidence; read the instructions closely.