Speaking with reporters at the State Department in Washington Tuesday, Kerry said "the ongoing crisis" in the region "continues to trouble all of us greatly."
"We are convinced that we have to help the parties find a path to a lasting peace, to a permanent cessation of hostilities and to the disarmament and demobilization of M23, accountability for human rights abuses and finally a breaking down of the barriers that are standing between humanitarian aid and the civilians who need it."
M23 is a rebel military organization also referred to as the Congolese Revolutionary Army.
Kerry said the region is "a high level priority" for him and President Barack Obama.
He said Feingold, a Democrat, was "the Senate's leading advocate and expert on Africa" during his time in office.
"I'm very grateful that he has agreed to come back to government and to apply the expertise that he gained those years for the Obama administration and for the State Department."
In his new role, Feingold will work on issues including cross-border security, and political, economic and social assistance, Kerry said.