Thomas Piketty (French: [tɔmɑ pikɛti]; born 7 May 1971) is a French economist who is a professor of economics at the School for Advanced Studies in the Social Sciences, associate chair at the Paris School of Economics (PSE) and Centennial Professor of Economics in the International Inequalities Institute at the London School of Economics (LSE).

Piketty's work focuses on public economics, in particular income and wealth inequality. He is the author of the best-selling book Capital in the Twenty-First Century (2013), which emphasises the themes of his work on wealth concentrations and distribution over the past 250 years. The book argues that the rate of capital return in developed countries is persistently greater than the rate of economic growth, and that this will cause wealth inequality to increase in the future. Piketty proposes improving the education systems and considers diffusion of knowledge, diffusion of skills, diffusion of idea of productivity as the main mechanism that will lead to lower inequality. In 2019, his book Capital and Ideology was published, which focuses on income inequality in various societies in history. His 2022 A Brief History of Equality is a much shorter book about wealth redistribution intended for a target audience of citizens instead of economists.

Piketty was born in the Parisian suburb of Clichy, Hauts-de-Seine. His parents had been involved with a Trotskyist group and the May 1968 protests in Paris but they had moved away from this political position before Piketty was born. A visit to the Soviet Union in 1991 was enough to make him a firm "believe[r] in capitalism, private property and the market".

Piketty earned a C-stream (scientific) Baccalauréat, and after taking scientific preparatory classes, he entered the École Normale Supérieure (ENS) at the age of 18 where he studied mathematics and economics. At the age of 22, Piketty was awarded his PhD for a thesis on wealth redistribution, which he wrote at the LSE and EHESS under Roger Guesnerie and winning the French Economics Association's award for the best thesis of the year. He also met Daron Acemoglu for the first time at the LSE, who was also a PhD student at the time.

After earning his PhD, Piketty taught from 1993 to 1995 as an assistant professor in the department of economics at the Massachusetts Institute of Technology. In 1995, he joined the French National Centre for Scientific Research (CNRS) as a researcher, and in 2000 he became a professor (directeur d'études) at EHESS.

Piketty won the 2002 prize for the best young economist in France, and according to a list dated 11 November 2003, he is a member of the scientific orientation board of the association À gauche, en Europe, founded by Michel Rocard and Dominique Strauss-Kahn.

In 2006, Piketty became the first head of the PSE, which he helped organize. He left after a few months to serve as an economic advisor to Socialist Party candidate Ségolène Royal during the 2007 French presidential election. Piketty resumed teaching at the EHESS and PSE in 2007.

He is a columnist for French center-left-leaning newspaper Libération and regularly writes op-eds for left-leaning newspaper Le Monde.