This is a question I get from families navigating both cultural tradition and legal compliance simultaneously, since cousin marriages remain a recognised and even preferred practice in certain communities and regions of India, while being considered prohibited in others, and the legal answer genuinely depends on the specific relationship and the customary practices of the community involved. Under codified Hindu law, the general rule is that marriage between first cousins is prohibited as falling within "degrees of prohibited relationship," but this general prohibition is subject to an important customary exception that makes the actual legal position considerably more nuanced than a simple yes or no.

The governing statute is the Hindu Marriage Act, 1955, and Section 5 of this Act lays down the essential conditions for a valid Hindu marriage, with Section 5(iv) specifically stating that the parties should not be within the "degrees of prohibited relationship" unless the custom or usage governing each of them permits such a marriage. "Degrees of prohibited relationship" is itself defined under Section 3(g) of the Act, and this definition includes relationships such as lineal ascendants and descendants, and relationships where one was the wife of a specified relative of the other, and importantly, it also covers relationships between children of siblings, which is precisely the category that first cousins fall into, meaning first-cousin marriages are technically within the prohibited degree under the default statutory framework.

However, Section 5(iv) itself carves out a crucial exception: if a custom or usage governing either party to the marriage permits marriage between persons falling within these prohibited degrees, such a marriage remains legally valid despite the general prohibition. This customary exception has real practical significance in India, since cousin marriages, particularly marriages between a person and their maternal uncle's daughter or, in some communities, paternal aunt's children, are a long-established, socially accepted, and even preferred practice in several South Indian communities, including among certain Tamil, Telugu, Kannada, and other communities that follow the Dravidian kinship system, where cross-cousin marriage has deep customary roots recognised by courts as valid usage under Section 5(iv). By contrast, in most North Indian Hindu communities, where the Aryan or Indo-Gangetic kinship framework generally prevails, first-cousin marriage carries no such customary sanction and would fall squarely within the prohibited degree, rendering it void and legally invalid under Section 5(iv) read with Section 11 of the Act, which specifically declares marriages performed in contravention of Section 5(iv), among other conditions, to be void.

Courts examining the validity of a specific cousin marriage will therefore look closely at whether the parties belong to a community with an established, provable custom permitting such unions, and the burden of proving this custom, meaning that it is ancient, certain, reasonable, and continuously and consistently observed within the community, generally rests on the party asserting the custom's existence. This is where these cases often become evidentiary in nature, requiring proof through community records, prior instances of similar marriages within the family or community, testimony from community elders, or documented customary practice, rather than a simple assertion that "our community allows this."

The practical consequence of a marriage falling within the prohibited degree without a valid customary exception is significant: under Section 11 of the Hindu Marriage Act, such a marriage is void ab initio, meaning it is treated as though it never legally existed, and either party can seek a formal declaration of nullity under Section 11 through a decree of the court, though even without such a decree, the marriage carries no legal validity from the outset. This has serious downstream consequences for issues like inheritance rights, legitimacy of children, and matrimonial remedies like maintenance or divorce, since a void marriage does not create the legal relationship of husband and wife in the eyes of the law, though children born from such a union are generally protected and treated as legitimate under Section 16 of the Hindu Marriage Act, which specifically safeguards the legitimacy of children born from void or voidable marriages regardless of the marriage's ultimate legal status.

Given how heavily the validity of a specific first-cousin marriage depends on proving an established community custom, and how significant the consequences of getting this wrong can be, both for the couple and for any children of the marriage, I strongly recommend that families considering such a marriage seek legal advice and, where necessary, proper documentation of customary practice before the marriage takes place, rather than assuming validity based on community tradition alone. You can reach out via Aapka Legal Advice for a careful assessment of whether your specific community's customary practice would be recognised under Section 5(iv) of the Hindu Marriage Act, and for guidance on documenting this custom appropriately to protect the marriage's legal validity. Aapka Legal Advice's panel of retired judges, alongside experienced family law practitioners, brings valuable insight into how courts have historically assessed customary marriage practices across different Indian communities. If a dispute has already arisen regarding the validity of a cousin marriage, whether concerning inheritance, maintenance, or legitimacy of children, the Top Criminal Lawyers in India | Aapka Legal Advice directory alongside the broader team at Aapka Legal Advice can help you engage counsel experienced in family law litigation involving these questions.

In summary, marriage between first cousins is prohibited by default under Section 5(iv) read with Section 3(g) of the Hindu Marriage Act, 1955, as falling within the degrees of prohibited relationship, but remains legally valid where an established community custom permits it, a recognised exception applied particularly to certain South Indian communities following cross-cousin marriage traditions. Where no such custom exists or can be proven, a first-cousin marriage is void under Section 11 of the Act, carrying serious consequences for inheritance and matrimonial rights, though the legitimacy of any children remains protected under Section 16, which is exactly why families considering such a marriage should seek proper legal guidance to confirm and document their community's customary standing before proceeding.