Correspondent Garland Nixon, co-host of Fault Lines on Radio Sputnik, was at the scene, and reported that Code Pink, an advocacy group, led the rally.
Medea Benjamin, co-founder of Code Pink, spoke at the event, stating that American citizens are unaware of their government's actions.
"I think anybody who cares about the truth, who cares about what our governments are doing in our name, who cares about war and peace issues and would like to see a lot more peace in the world, should be appalled at the incarceration of Julian Assange," Benjamin told demonstrators.
Benjamin honed in on the role played by journalists during the the US-led invasions of Iraq and Afghanistan. She mentioned Judith Miller's reporting on the alleged existence of weapons of mass destruction in Iraq for the New York Times, to which the crowd responded with chants of, "Boo" and "Liar."
Benjamin also credited WikiLeaks for shedding light on the imprisonment and detention of innocent people at the US military's Guantanamo Bay Naval Base in Cuba.
Protestors also held up signs calling for Assange's release.
Passing drivers showed support for the protestors "by tooting their horns, rolling down their windows, giving the thumbs-up sign," noted Nixon.
More recently, Manning was jailed for refusing to testify before a grand jury about her role in handing over information to Assange. After a month in solitary confinement, she was moved to the general population jail in Alexandria, Virginia.
Since his arrest, Assange has been charged by US authorities with allegedly aiding Manning in hacking government computers to acquire some of the files she handed over to WikiLeaks. British courts also found him guilty of breaching his 2012 bail conditions.
Assange is expected to face an extradition hearing in May in a UK court.
Kilbride went on to refer to Secretary of State Mike Pompeo, President Donald Trump and Hillary Clinton as "war criminals and liars."
There were a dozen or so DC police officers at the event.
Nixon noted that the protest's theme included Manning's recent arrest as well, noting, Manning is "an integral part of this conversation."