The United States will next take steps to immediately overturn remaining charges against Assange in the Eastern District of Virginia, the report said.
Assange's guilty plea concludes a criminal prosecution against him, but he is not allowed to return to the United States without permission, the US Department of Justice confirmed in a release.
"The guilty plea concludes a criminal matter that dates back to March 2018 ... Following the imposition of sentence, he will depart the United States for his native Australia. Pursuant to the plea agreement, Assange is prohibited from returning to the United States without permission," the Justice Department's statement read.
The US court ruled that no harm was caused by Wikileaks founder Assange's publications, Assange’s lawyer told media.
"WikiLeaks's work will continue and Mr. Assange, I have no doubt, will be continuing force for freedom of speech and transparency in government," chief US lawyer Barry J. Pollack said outside court, the Australian news agency ABC reported.
"The prosecution of Julian Assange is unprecedented in the 100 years of the espionage act," Pollack added.
"It has never been used by United States to pursue a publisher, a journalist, like Mr Assange,” the lawyer emphasized.
"I believed the First Amendment protected that activity. I believe the First Amendment and the Espionage Act are in contradiction," Assange said when asked to explain the charge against him in his own words, the Australian channel ABC reported.
"Working as a journalist I encouraged my source to provide information that was said to be classified in order to publish that information," the news agency cited Assange.
He explained he was pleading guilty because fighting the case in court would be challenging, according to the report.
US attorney Matthew McKenzie said the US would move to dismiss the indictment in the Eastern District of Virginia, the report said.
A plane with WikiLeaks founder Julian Assange on board has departed for Australia's capital, Canberra, from the Northern Mariana Islands, Australian broadcaster ABC reported.
Assange, an Australian citizen, was transferred to London’s high-security Belmarsh prison in April 2019 on bail breach charges. In the US, he faced prosecution under the Espionage Act for obtaining and disclosing classified information that shed light on war crimes and human rights violations committed by US troops in Iraq and Afghanistan.