When you need it
A married person who needs a general sworn statement confirming their marriage — its date, place and the fact that it took place — for a bank or joint account KYC update, an employer's personnel records, adding a spouse as an insurance nominee or dependant, a child's school or college admission, a housing society or utility record, or any other counter that asks for proof of marriage and will accept a notarised affidavit rather than, or in addition to, a marriage certificate. Also useful where the marriage was solemnised long ago by custom or religious rite and was never formally registered, or where registration is still pending and something is needed in the meantime.
Not for: the age-and-marital-status affidavit filed before a Marriage Officer to arrange a court marriage under the Special Marriage Act, 1954 (use the Court Marriage Affidavit in this library instead); a passport application specifically (use the Passport Annexure Affidavit or the Passport Spouse Name Addition Affidavit); registering the marriage itself with the Registrar (use the Marriage Registration Application); or changing your own name after marriage (use the Name Change after Marriage Affidavit).
Punjab and Chandigarh: sworn before a Notary Public or an Oath Commissioner, then produced directly at the counter that needs it.