As of 2015, a citizen of the United Kingdom can become an American citizen after five years of permanent residency or through marriage, employment or asylum, according to the U.S. Citizenship and Immigration Services. Specific rules apply, and exceptions are made in some cases.
Any United Kingdom citizen who is at least 18 years old and has maintained a permanent residency in the United States for at least five years, or three years in special circumstances, may apply for U.S. citizenship, explains the USCIS. Those who have maintained permanent residency in the United States for at least three years are eligible for citizenship if they are married to a U.S. citizen, if their spouse has been a U.S. citizen for at least three years, and if they have remained in the country for at least 18 months of the three-year period.
Those who have maintained permanent residency for at least five years need to prove their allegiance to the United States and that they have not left the country for 30 months or more during their permanent residency status, states the USCIS. In addition, the person must not have left the United States for a year or longer during the permanent residency period without a Form N-470.
Additional ways for foreign citizens to gain permanent residency in the United States is through a marriage green card, an employer visa sponsored by a U.S. business, or through applying for asylum, according to the USCIS. The United States allows dual citizenship with many countries, although some foreign countries require foreigners to renounce their citizenship before becoming U.S. citizens. The United Kingdom is one country that allows dual citizenship with the United States.