Sahara, a household name in India through its sponsorship of the national cricket team, sought a review of a Supreme Court order to refund about Rs 24,000 crore to investors.
In August, the court ruled that the finance schemes run by two Sahara companies were illegal - confirming an order by the Securities and Exchange Board of India, the markets regulator.
The court told Sahara, an unlisted conglomerate, on Friday to repay the money, plus interest, to almost 30 million mostly small investors within 90 days.
Although companies often file review petitions when the top court's judgment goes against them, it is rare for the court to change its decision.
Sahara has not said how it will refund the money, although it has said it is healthy and investors need not worry.
The company, which also has interests in hotels, including a recent deal in New York, was not immediately available to comment on Friday.