The chairs held a conference call after President Joe Biden announced he was stepping aside as the party's candidate.
“Following President Biden’s announcement, our members immediately assembled to unite behind the candidate who has a track record of winning tough elections, and who is a proven leader on the issues that matter to Americans: reproductive freedom, gun violence prevention, climate protection, justice reform, and rebuilding the economy," said Ken Martin, president of the Association of State Democratic Committees, in a statement.
"That person is our sitting Vice President Kamala Harris."
Reuters reported earlier that the group had backed the vice president, with one source saying there was "full support" for her being at the top of the ticket.
Many Democrats quickly backed Harris to run as the party's presidential nominee against Trump in the November election, but some powerful party members, including former House of Representatives Speaker Nancy Pelosi, stayed quiet.
