Between 2011 and 2013, Harris worked at the White House as a senior economist with the Council of Economic Advisers, where he specialized in fiscal policy and retirement security.

After leaving his first stint with the Obama administration, he served as a senior research associate with the Urban Institute and the Urban-Brookings Tax Policy Center.

In December 2014, Harris returned to the White House when Vice President Joseph R. Biden Jr. tapped him to serve as his chief economist and economic advisor.

[14][8][15] Harris was one of the campaign's most active surrogates, and was named a member of the Biden-Sanders Unity Task Force, serving as one of Biden's five delegates on the economic policy committee.

[20][21] On March 11, 2021, President Joe Biden announced his intent to nominate Harris to be Assistant Secretary of the Treasury for Economic Policy.

[24] During his time with the Treasury Department, Harris was widely recognized as a principal official driving the creation and implementation of the price cap on Russian oil.