African Americans will be a key constituency in the Democratic contest once it moves beyond New Hampshire, which is predominantly white, much like Iowa, where Clinton narrowly prevailed Monday in the first-in-the-nation caucuses.
Though Sanders has a long history of civil-rights activism, he began his presidential bid largely unknown among black voters. About 95 percent of Vermont's population is white.
Clinton has enjoyed large leads in polling among African Americans, as well as the endorsements of a broad array of black elected officials.
The planned endorsement by Jealous was first reported by CNN. The person who confirmed it requested anonymity because the campaign is not ready to formally announce its new backer.