Bankia, which was bailed out in 2012, is accused of misrepresenting its accounts ahead of the listing, and thousands of customers who say they lost their money after being misled into converting their savings to shares have brought separate lawsuits against the group.
Associations representing those affected say that in several hundred cases, judges ruled in their favour.
The Supreme Court on Wednesday ruled on just two cases that Bankia had appealed against, in which courts decided that the listing's information leaflet did not reflect the bank's true situation and ordered it to pay the money back.
The ruling confirmed the courts' decisions, paving the way for more compensation claims just as Spain's National Court investigates former IMF head Rodrigo Rato, who was chairman of Bankia at the time, along with other suspects.
The Supreme Court ruled that those who brought shares were led into error "due to the serious inaccuracies of the public offer's leaflet."
Bankia and its parent company BFA said in December they had set aside €1.8 billion in provisions for claims that by the end of 2014 already stacked up to €819 million.