WASHINGTON—The Senate confirmed Jacob Lew Wednesday as the country's 76th Treasury secretary, making him one of President Barack Obama's top representatives in battles over looming spending cuts, taxes and other economic policy issues.

The Senate voted 71-26 to confirm Mr. Lew, with 20 Republicans joining all the Democrats present, despite earlier concerns raised by some in the GOP about the nominee's time in the private sector. Independent Sen. Bernie Sanders of Vermont joined the other Republicans voting against Mr. Lew....