3rd cousin marriage, perspectives.

It basically depends on your family. But as per the customs in the society, not all cousins marriages are allowed as per hindu customs. Mostly in hindu religion, marriages between paternal and maternal cousins are usually prohibited. Marriages between cousins in same family, father's brother and mother's sisters children are strictly prohibited. But sometimes, marriages with father's sisters children may be allowed. As she is your 3rd cousin, and if you both are agree then there should be no problem.

Further, If your family will not agree on this marriage, you can go for court marriage or arya samj marriage.

In certain regions and customs, marriage between cousins is allowed in India. According to the Hindu Marriage Act of 1955, marriage between cousins is considered illegal for Hindus. However, the exception is given if regional customs allow it. For example, in Southern India and Maharashtra, marriage between cousins is allowed because their customs allow it. In the rest of India, it is seen as incest.

Since you are from Tamilnadu where cousin marriages are allowed, I don't think there will be a problem if you marry your cousin. However, the marriages between cross cousins are allowed. If she was your father's sister's daughter, you might not face any difficulty. Since she is your father's brother's daughter, I don't feel it is legal. You need to confirm it from a lawyer before you proceed with your proposal. Or talk to your elders to know whether such marriages are allowed in your custom. If your custom permits it, it is legal too.

As far as legality is concerned marrying the third cousin is allowed. There will be no problem. If both of you are majors now and if you both agree legally there will not be any objection.

But two things you have to consider is the family opinion and religious beliefs. She is your father's second cousin brother's daughter. As per the relation, she will be your sister. Hindu religion will never accept this marriage. But these days people are not much worried about this relation. Your surname and her surname will be the same. Marrying people with the same surname is also not allowed as per the Hindu religion.

What is the opinion of her parents and your parents? Are they agree with this proposal? Even though they don't agree, are you ready to marry that girl? Is she ready for the marriage, even though her parents do not agree?

Once you think above matter and even then you both decide to marriage go ahead.

As per Hindu mythology, cousins are not accepted for marriage since the origin of the great grand father or vice versa is all the same and they are supposed to be close relative. This law is still valid in the Hidu - community except the region of South - India.
In your case, you being from TN, you can go ahead for the negotiation because of acceptance of such alliance.
However, for the peace and lasting relationship, you should take consent of both the parties and see if there is any divergence of their opinions. This needs to be resolved in case of disagreement from different circles so that accept this marriage negotiation ultimately.
Before you proceed for such negotiation, get yourself genes test done including your fiancé so as to avoid any health hazards relating to Heart - problem, High Blood Pressure, Diabetes etc of you couple since the marriage between the close relationship invites such problems.

The first cousin marriages are termed as illegal as per the Hindu Marriage Act, 1955. If the cousin are cross cousin then it is not considered illegal. There is some scientific reasoning also as there are some disease making hereditary transfers from one generation to another which may lead to medical complications in first cousin marriage. A person shares a third cousin relationship with the children of his parents second cousins. So the third cousins will share at least one set of great-great-grandparents. The Hindu Marriage Act does not restrict marrying in second and third cousin. Also, there are no serious medical apprehensions in the second and third cousin marriages.

Another interesting thing in the above Hindu law is that if there is a tradition of marrying in first cousin then this law will not be applicable to that particular community. They can go ahead in this matter as per their customs.

In India, there are three aspects of a marriage. The first one is legal. As per the legal position, you can marry your third cousin. There is no legal bar to it. The second aspect of marriage is family and society. I don't know about your family and relatives. Will they accept such marriage? Are there precedences of such marriage in your near or distant relations. The societal reaction would depend on these aspects.

However, if you and your partner are compatible and both are economically self-dependent, then you can go for it, even if the family and relatives are opposed to this idea.

Times have changed. Whether it is allowed or not, if you produce children with some hereditary defect, they can sue you for creating them after being aware of fact consanguineous unions has genetic issues. You've got to seriously think and discuss before going ahead.