The blaze, in which 75 people were also injured, happened at a venue near the famous Srirangam Hindu temple in Tiruchchirapally, about 300 kilometres from the Tamil Nadu state capital Madras.
The blaze was started by the holy fire the bride and the groom walk around seven times to solemnise their wedding vows according to Hindu religious customs, a police official said.
It then whipped through the crowded hall, which was decorated with dried coconut palm leaves, and caused the short-circuiting of electricity cables.
The dead included the 28-year-old groom, who worked for a government-run insurance company, 28 women and four children.
The bride escaped unhurt as she was still preparing for the wedding ceremony.
Some of the 75 injured were in a serious condition and the death toll could rise, the official said.
The blaze has been brought under control and firemen were removing the bodies of victims, he said.