The Senate confirmed Ms. Yellen, a long-time Fed official and economist at the University of California at Berkeley, by a 56-26 vote on Monday.

Janet Yellen will take the helm of a Federal Reserve facing a significantly different economic landscape than the one that dominated Ben Bernanke’s tenure as chairman, confronting her with different decisions as well.

Mr. Bernanke’s eight years leading the Fed were largely consumed with the Great Recession and his efforts to cure it by pushing down interest rates and pumping cash into the economy. Many economists think Ms. Yellen’s big challenge will be deciding how to ease off some of those very policies, which Mr. Bernanke took with her support.

“Circumstances may demand more rapid tightening than people are expecting,” said Bill Cheney, chief economist for John Hancock Financial Services, who envisions a growing economy this year. He contrasted that with Mr. Bernanke, who he said had to decide “when to step on the gas pedal and how hard” as the economy recovered weakly from the recession.

The Senate confirmed Ms. Yellen, a long-time Fed official and economist at the University of California at Berkeley, by a 56—26 vote on Monday. Supporting her were all 45 voting Democrats and 11 Republicans, while all opposing votes came from the GOP. Many senators missed the vote because frigid weather canceled numerous airline flights.

Ms. Yellen begins her four-year term on Feb. 1, when Mr. Bernanke steps down. She has been Fed vice chair since 2010.

Nominated by President Barack Obama to the top job in October, Ms. Yellen comes to the post after a career in which she has focused in part on unemployment and its causes. Obama and congressional Democrats lauded her concerns for workers on Monday.

In a written statement, Mr. Obama said Ms. Yellen’s approval means “the American people will have a fierce champion who understands that the ultimate goal of economic and financial policymaking is to improve the lives, jobs and standard of living of American workers and their families.”

Many Republicans were less enthusiastic. Sen. Charles Grassley warned that a continuation of the Fed’s easy money policies “risks fueling an economic bubble and even hyper-inflation,” which he said could cause “real and lasting damage to our economy.”

Lobbyists for the banking and financial services sectors issued statements pledging to work with Ms. Yellen. Both industries have led a fight to water down restrictions imposed by Mr. Obama’s 2010 law overhauling how the nation’s financial system is regulated.

The Fed announced in December that the labour market has improved enough that it will begin reducing its $85 billion in monthly bond purchases, starting with a $10 billion reduction this month. It has pushed that money into the economy to try keeping long-term interest rates low.

But Ms. Yellen will face questions about how to manage that process. Moving too fast could spook financial markets and shove interest rates higher, while withdrawing the bonds too slowly could risk creating bubbles that might burst in real estate, the stock market or other assets.

The bond purchases have ballooned the Fed’s holdings over $4 trillion. That leaves Ms. Yellen with decisions about how to wind down the central bank’s balance sheet to a smaller, more normal level without destabilizing financial markets used to the huge cash infusions.

Ms. Yellen also will have to decide when and how to ease off short-term interest rates, which the Fed has kept near zero since December 2008. To assure investors that those rates won’t precipitously rise, the Fed has repeatedly issued statements saying that policy will continue.

Last month, the Fed said the low rates will continue “well past” when the unemployment rates falls to 6.5 percent. Unemployment was 7 percent in November and many economists think the low interest rates will last until late 2015.

Ms. Yellen will also guide the Fed at a time when some Republicans say the central bank needs to be more accountable to Congress. Last week, Mr. Bernanke voiced concerns about legislation giving the Government Accountability Office, Congress’ auditing arm, more power to examine how the Fed makes interest rate decisions. Mr. Bernanke said such legislation would make it harder to assure markets that its decisions aren’t influenced by political pressure.