Muslims are allowed to marry more than one wife even while living in Western countries. Through consenting a nikah, a woman becomes a man’s wife. It is not necessary for the marriage to be registered with the local government for it to be an Islamically legitimate marriage. Hadrat Khalifatul-Masih IV rta said:
No country can implement laws against polygamy. The reason is that the moral standards of the countries that have laws restricting polygamy have fallen to such an extent that according to them it is not illegal even if a person keeps fifty women. The only condition is consent of both parties, and this is the law in effect in these countries. Thus, from the perspective of Islam, if a person has married four wives, their law will consider one as a wife and the rest as mistresses. They have a strange position: as far as rights go, wives are being given the status of mistresses and mistresses are being given the status of wives. Thus, it makes no difference, let them say what they want to say.
(Urdu Mulaqat Session, no. 22)
Hudur rta explained that when Hadrat Musleh Mau‘ud ra traveled to Europe, he brought all of his wives with him. When preparing for the journey, the question arose as to how they would be able to come, since according to the laws of Europe, they would only accept one as a wife. Hadrat Musleh Mau‘ud ra said that:
I did not care for their laws. It is not a crime to keep a woman with you, so if God has given me permission to keep her, then what do I care what they consider her status to be. It is Allah who will decide what her status is, or my heart that will decide whether my decision is according to the command of Allah or not.
(Urdu Mulaqat Session, no. 22)
Hadrat Khalifatul-Masih IV rta said:
No, they can… There is no such country to my knowledge where they do not permit to have more than one wife. Legal wife yes, but illegal wife you can have hundreds, there is no problem. You see, a Muslim can take the posture that this woman, according to you, is not a wife. Alright, call her a mistress, but in the sight of my God, she is a wife. No problem.
(Majlis Irfan, July 2, 1991)
The primary precondition is that a person does justice, which is a difficult standard. If a man can fulfill the condition of justice, he has the right to marry.
If it is necessary for someone to marry more than one wife, but resides in a country where marrying multiple wives is illegal, he may seek advice from the Jama‘at explaining his circumstances. The Jama‘at does not prohibit Ahmadis from having multiple wives in the West. Also, in a recent case in Utah, a Federal Judge has set a legal precedent in the United States that families with multiple wives who live together but do not seek more than one marriage license cannot be prosecuted.