For Registration of Marriages which have already been solemnized, following documents are required:

(1) Application form duly signed by both husband and wife.
(2) Documentary evidence of date of birth of parties (Matriculation Certificate / Passport / Birth Certificate). Minimum age of both parties is 21 years for male and 18 years for female, at the time of registration under the Special Marriage Act / Hindu Marriage Act.
(3) Ration card of husband or wife, at least one should be resident of Delhi for 30 days.

(4) In case of Special Marriage Act, documentary evidence regarding stay in Delhi of the parties for more than 30 days (ration card or report from the concerned SHO, Police Station). (NOTE: Delhi High Court in Vikram Aditya Singh & others Vs. UOI & others, CW15079/2006 held that this condition in Delhi Hindu Marriage Registration Rules, is ultra vires and solemnisation is sufficient for registration; see other case - Seema Vs Ashmin Kumar 2006 2SCC 578).
(5) Affidavit by both the parties stating place and date of marriage, date of birth, marital status at the time of marriage and nationality.
(6) Two passport size photographs of both the parties and one marriage photograph.
(7) Marriage invitation card.
(8) If marriage was solemnized in a religious place, a certificate from the priest is required who solemnized the marriage.
(9) Affirmation that the parties are not related to each other within the prohibited degree of relationship as per Hindu Marriage Act or Special Marriage Act as the case may be. For details of such relationships please read below at end.
(10) Attested copy of divorce decree/order in case of a divorcee and death certificate of spouse in case of widow/widower.
(11) In case one of the parties belong to other than Hindu, Budhist, Jain and Sikh religions, a conversion certificate from the priest who solemnized the marriage (in case of Hindu Marriage Act).

All documents excluding receipt should be attested by a Gazetted Officer.

Process
For registration under Hindu Marriage Act

Verification of all the documents is carried out on the date of application and a day is fixed and communicated to the parties for registration. On the said day, both parties, along with witness should attend office of marriage officer. The Certificate of Marriage is issued on the same day.