Harris plans to rally for the Jealous campaign, a spokesman for the campaign said.
The former NAACP president has received a steady flow of endorsements from progressive groups and national progressive leaders.
Harris, who has become a leading voice on immigration reform and a rising star in the Democratic Party, joins U.S. Sen. Cory Booker (D-N.J.) and U.S. Sen. Bernie Sanders (I-Vt) in backing Jealous’s bid in the crowded primary.
He has also received backing from key progressive groups in the state, including Progressive Maryland, the Service Employees International Union and Maryland Working Families. Jealous has been slow to receive the same type of support from the Democratic establishment.
Jealous, who is making his first run for political office, continues to trail other Democratic candidates in the polls. A recent Mason-Dixon poll found Prince George’s County Rushern L. Baker III leading the primary field at 26 percent, followed by Baltimore County Executive Kevin Kamenetz, 15 percent, and Jealous, 14 percent.