Section 24 of the Special Marriage Act, 1954 deals with void marriages.

Any marriage solemnized under the Act is null and void (and may, on a petition presented by either party thereto against the other party, be so declared) by a decree of nullity if:

1. Either party has a spouse living
2. Either party:
   • is incapable of giving a valid consent to it in consequence of unsoundness of mind, or
   • though capable of giving a valid consent, has been suffering from mental disorder of such a kind or to such an extent as to be unfit for marriage and the procreation of children or
   • has been subject to recurrent attacks of insanity or epilepsy
3. the male has not completed the age of twenty-one years and the female the age of eighteen years
4. the parties are within the degrees of prohibited relationship unless a custom governing at least one of them permits of a marriage between them
5. the respondent was impotent at the time of the marriage and at the time of the institution of the suit.

This does not apply to any marriage deemed to be solemnized under the Act within the meaning of Section 18.

Under Section 18 which speaks of the effect of the registration of a marriage under the Special Marriage Act, where a certificate of marriage has been finally entered in the Marriage Certificate Book under the Act, the marriage shall, as from the date of such entry, be deemed to be a marriage solemnized under the Act, and all children born after the date of the ceremony of marriage (whose names shall also be entered in the Marriage Certificate Book) shall in all respects be deemed to be and always to have been the legitimate children of their parents.

However, the registration of any a marriage deemed to be solemnized under the Act within the meaning of Section 18 may be declared to be of no effect if:

1. a ceremony of marriage has not been performed between the parties and they have not been living together as husband and wife ever since
2. either party had more than one spouse living at the time of registration
3. either party was an idiot or a lunatic at the time of registration
4. either party had not completed the age of twenty-one years at the time of registration
5. the parties were within the degrees of prohibited relationship although, in case of a marriage celebrated before the commencement of the Act, this condition is subject to any law, custom or usage having the force of law governing each of them which permits their marriage.

A declaration that a marriage is void cannot be made in any case where an appeal against an order of a Marriage Officer refusing to register a marriage celebrated in another form has been preferred and the decision of the Court has become final.