An investigation by the British broadsheet found there was little evidence in the 43-year-old's original sources to underpin his argument that an increasing share of total wealth is in the hands of the richest.
The English-language version of the heavy tome, "Capital in the Twenty-First Century", topped the bestseller list on Amazon in the United States and has sparked a political debate about the gap between rich and poor.
Critics have tried to deride his work by labelling him a neo-Marxist, but it gained him an audience at the White House last month with top economic advisors to US President Barack Obama.
Piketty uses data from the past two centuries across 20 countries to demonstrate how inherited wealth has ensured the dominance of a small class of people and will continue to do so unless action is taken.
He rejects the widely-held argument that economic growth in the capitalist system benefits everyone, and advocates a punitive global tax on wealth to address the problem.
However, "once the FT cleaned up and simplified the data, the European numbers do not show any tendency towards rising wealth inequality after 1970," the Financial Times' report said.