Jack Lew began his career as a legislative aide in 1973 and later held key budget positions with Presidents Obama and Clinton.
He also worked as an investment banker.
Lew has a reputation as a tough negotiator with a keen understanding of the details of the immense U.S. budget.
That reputation is likely to be tested in the coming months, as Congress and the White House battle over the federal budget and a rapidly expanding debt.
Four years ago, when U.S. central bank official Timothy Geithner was sworn in as Treasury Secretary, unemployment was rising and the stock and housing markets were in danger of collapse.
Geithner helped the departing Bush administration and the new Obama administration use $700 billion dollars to prop up tottering financial firms in a bid to reassure investors, businesses and consumers.
Despite much criticism, economist Desmond Lachman of the American Enterprise Institute says the program worked.
"The country was facing a huge crisis, many people thought we could quite easily tip into a depression , he managed to stabilize that situation," Lachman said.
But Lachman and other critics say Geithner did too little to improve the day-to-day growth of the economy.
"He favored Wall Street on far too many occasions at the expense of Main Street," Lachman said.
Sarah Anderson at the Institute for Policy Studies hopes for a new approach at the Treasury Department.
"Three things to look for in the next Treasury Secretary:
Are they going to be more aggressive in reining in Wall Street?
Are they going to do more to help homeowners facing foreclosure?
And are they going to be a deficit hawk or are they going to try to get our economy back on its feet before they address the deficit?" Anderson said.
The coming two months will be a test for Lew, as the battle over the budget deficit heats up in Congress.
Although stock markets, housing and the banking industry have stabilized, economists warn the US economy remains fragile.
Without a budget deal in Congress, many say the US recovery could stall.
The legislative system needs reforming.
This store has an excellent reputation for fair dealing.
Mass unemployment may lead to social upheaval.
She managed to totter back to her seat.
He suffers from acute depression.