Kanyadaan is an important ceremony in Hindu marriage. It is mandatory for a marriage to be held valid:

Section 7 HMA permits solemnisation according to the customary rites and ceremonies of either party. It does not prescribe kanyadaan as an indispensable ceremony for every Hindu marriage. Where a particular applicable custom requires rites, those rites must be considered; the general statement that every valid Hindu marriage needs kanyadaan is therefore false. The identity of the person performing it does not turn it into a universal statutory requirement.