Mr. Williamson attended the London School of Economics, graduating with a degree in economics in 1951. After completing two years of compulsory military service, he entered graduate school at Princeton, where he received his Ph.D. in 1963.
Though he had frequent offers from Oxford and Cambridge, especially later in his career, Mr. Williamson was drawn to the sort of creative research being done at some of the newly established, so-called plate-glass universities, after their modernist architecture.
He joined the University of York in 1963, the year it was founded, and later taught at the University of Warwick, founded in 1965. But he was increasingly drawn to policymaking. In 1968 he took a job as an adviser to the British Treasury, where he worked on economic relations with the European Economic Community, and later moved to Washington to work at the International Monetary Fund.
While at the I.M.F. he met Denise Rausch, a Brazilian economist. They married in 1974.
Along with his daughter and wife, Mr. Williamson is survived by two sons, Andre and Daniel; two sisters, Chris Evans and Wyn Jones; and seven grandchildren.
The Williamsons spent the late 1970s in Brazil, where she worked for a research institution and he taught at a Catholic university. Ms. Williamson taught her husband Portuguese, something he considered his greatest achievement, having struggled with foreign languages in school.
They returned to Washington in 1981, when the economist C. Fred Bergsten hired Mr. Williamson to be the first employee of the newly founded Institute for International Economics, later renamed the Peterson Institute for International Economics. He remained there until he retired in 2012. (In 1996 he took a leave from the institute to join the World Bank, where his wife worked, though he left after just three years, frustrated with the bank’s bureaucracy.)
Until he coined the Washington Consensus, Mr. Williamson was best known for his work on exchange rates. He was a passionate advocate for a middle ground between the rigidity of fixed rates — especially for developing economies — and the chaos of floating rates, which he believed put even developed economies at the mercy of global financial markets.