Matthew Elliot served as chief executive of Vote Leave during the referendum campaign, and previously founded the TaxPayers' Alliance campaign group.
He will join Legatium as a senior fellow, exploring the possibilities of a UK-US trade deal and exploring the rise of populism.
Elliott said: “Brexit provides us with an opportunity to promote global prosperity by strengthening free trade, and the Institute is one of the only think-tanks with the skills and global reach to achieve this important objective.
"Clarity of thought is also required on the rise of populism, and I look forward to analysing the similarities and differences between public opinion in Britain and overseas."
He is the latest senior figure from the Vote Leave campaign to secure a high-profile role in the outside world.
The Brexit campaign's former communications director Paul Stephenson launched lobbying firm Hanbury Strategy in September, and chief spokesman Rob Oxley is now a special adviser at the Department for International Development.