For the groom — Indian or Western?
For most Indian grooms, in most Indian wedding ceremonies, ethnic dress — a sherwani, an achkan, or a Jodhpuri suit — is the appropriate choice. Indian weddings are ceremonies rooted in Indian tradition, and the groom's dress is the central visual statement of the ceremony. A Western suit at an Indian wedding ceremony reads as culturally uncertain — as though the groom has not committed to the tradition of the occasion.
The exceptions are meaningful: for an Indian Christian wedding where the ceremony format is closely aligned with Western Christian tradition, a Western morning suit or a fine dark suit is entirely appropriate and may even be more contextually correct than a sherwani. For a civil registry marriage or a courthouse ceremony, Western formal dress is the natural choice. For a destination wedding in a European or other non-Indian setting, a well-fitted Western suit can read as correctly formal in the local context while elements of Indian dress — a pocket square in sari cloth, a bandhgala for the reception — maintain the Indian identity.
For the wedding guest — the practical guide
Wedding guests have more flexibility than grooms. Both Indian ethnic dress and Western formal dress are typically acceptable at Indian weddings unless the invitation specifies otherwise. The choice should be guided by the nature of the ceremony (a traditional Hindu wedding benefits from Indian dress on guests; a Western-format reception is equally appropriate in a suit), the regional tradition of the hosts, and the wearer's personal comfort and identity.
The best approach for a wedding guest who wants to dress correctly rather than simply comfortably: if in doubt, choose Indian. Indian ethnic dress at an Indian wedding is never out of place; a Western suit at a very traditional Indian ceremony can read as disconnected from the occasion. Conversely, at a reception with a mixed Indian-Western guest list, a fine Western suit or a Jodhpuri suit — which reads from a distance as a Western suit while being clearly Indian up close — is a universally appropriate choice.