Kerry will formally announce Feingold's selection on Tuesday.
During his time in the Senate, Feingold served as the chairman of the Senate Foreign Relations subcommittee on African Affairs.
Feingold's name had previously been floated to serve as envoy to Africa. In an email to the Milwaukee Journal Sentinel in May he said he was open to the position.
"I would of course welcome the opportunity to work with Secretary Kerry and to serve my country and President," Feingold wrote to the Wisconsin newspaper.
The post is partially meant to help resolve conflict in the Congo where rebels and the country's government have been in negotiations since December. Those talks have been set back after new violence erupted in the North Kivu province of the Congo.