She also captured endorsements from Representative Alexandria Ocasio-Cortez and two Democratic presidential candidates, Elizabeth Warren and Bernie Sanders. Ms. Cabán thanked the Working Families Party and Democratic Socialists of America. The crowd chanted, “Black Lives Matter,” “People-powered justice,” and “No new jails.”

“I ran because for too long too many communities in Queens haven’t had a fair shot in the criminal justice system,” Ms. Cabán said.