He's the third French economist to be awared the prize, and the first for more than a quarter of a century. He's also a smidgen younger than the average awardee, at 61 (the usual age is 67).
Here's a biography from the European Coroporate Governance Institute. Though he's French, its a win for MIT too: Tirole took his PhD at the university, and has a visiting professorship there.
Here's the Nobel Committee's explanation of why they chose Tirole:
"Many industries are dominated by a small number of large firms or a single monopoly. Left unregulated, such markets often produce socially undesirable results – prices higher than those motivated by costs, or unproductive firms that survive by blocking the entry of new and more productive ones.
From the mid-1980s and onwards, Jean Tirole has breathed new life into research on such market failures. His analysis of firms with market power provides a unified theory with a strong bearing on central policy questions: how should the government deal with mergers or cartels, and how should it regulate monopolies?"