Three decades before he was tapped to lead the Treasury Department, Scott Bessent was asked to help break another country’s financial system.

Then 29 years old, Mr. Bessent, working for the financier George Soros, helped “break” the Bank of England with crushing trades against the British pound. He was on a small team at Mr. Soros’s investment firm that, in 1992, amassed a $10 billion bet that the pound was overvalued.

Though the British government tried to support the currency, it wasn’t able to withstand the pressure, and the pound plunged in value. Mr. Soros’s fund earned more than $1 billion, along with credit (and infamy) for orchestrating one of Wall Street’s most audacious trades.

When President-elect Donald J. Trump announced his selection of Mr. Bessent as Treasury secretary last week, there was no mention of the connection to Mr. Soros. But it was Mr. Bessent’s experience at Mr. Soros’s fund — including another high-profile bet, against the Japanese yen — that helped define his career, and that his former colleagues and other associates see as a crucial credential.

Mr. Bessent “could see the vulnerabilities in a way that most other people in the financial markets didn’t see,” said David Smick, an adviser to Mr. Soros at the time of the bet against the pound.

Mr. Bessent, 62, has spent nearly four decades as a trader or chief investment officer at hedge funds, including two stints running his own firm.