Brainard would replace White House National Economic Council (NEC) Director Brian Deese, who has announced his resignation.

In addition Biden confidant Jared Bernstein is expected to replace Cecilia Rouse as chair of the Council of Economic Advisers, the source said. Rouse has announced plans to depart.

The White House declined to comment.

Bloomberg News first reported the changes.

Markets' response was muted in Asia hours, with bonds and the dollar steady along with U.S. futures, and analysts said the implications of the appointment weren't very clear.

"We don't know what to infer from this," said Vishnu Varathan, head of economics at Mizuho Bank in Singapore.

"Under normal circumstances I would have thought that her advice to Biden would be very pro stimulus," he said.

"(But) the inflation backdrop will probably dampen if not check some of her underlying tendencies...I suspect that a lot of her input may be on the supply side."

Biden is making over his top economic team as the Fed continues to hike interest rates but the U.S. labor market remains tight, raising the prospect of an unusual recession without significant job losses.

The next NEC director and CEA chair will help shape the Democratic Biden administration's economic policy, from executive orders to congressional spending bills and raising the debt limit, in the face of a more hostile U.S. House of Representatives, now controlled by Republicans.

Brainard is a Harvard-educated Democrat who has been at the Fed for nearly a decade and served as Treasury's top international affairs expert under President Barack Obama. She was an economic adviser to then-President Bill Clinton.