• WikiLeaks gained international prominence in 2010 when the website released footage from a 2007 U.S. helicopter attack that killed two Reuters news staff and several others in Iraq's capital, Baghdad.
• The 52-year-old has been battling extradition for more than a decade.

The plane carrying Julian Assange, who has fought U.S. espionage charges for more than a decade for his whistleblowing efforts, landed in his homeland of Australia on Wednesday, according to a social media post from the WikiLeaks organization that he founded.

He was permitted to walk free after pleading guilty in a U.S. court in the Northern Mariana Islands, a U.S. commonwealth in the Pacific Ocean, to a felony charge for publishing U.S. military secrets.

According to documents from the U.S. court in Saipan, the largest island and capital of the Northern Mariana Islands, Assange pleaded guilty to one criminal count of conspiracy to obtain documents, writings and notes connected with the U.S. national defense and communicating these materials.

As part of the plea agreement, the U.S. is bound to withdraw its extradition request and has recommended a sentence equivalent to the time he already served in prison, with no additional fines issued.

"The chilling effect is the United States pursuing journalism as a crime," Assange's U.S. lawyer Barry Pollack said during a press briefing after the Saipan hearing. Pollack also warned that this sends a "chilling precedent."

He noted that Assange had acknowledged that he accepted and disclosed documents from Army intelligence analyst Chelsea Manning, and that, "unfortunately, that violates the terms of the Espionage Act" — a federal law instituted shortly after the U.S. entered World War I that oversees the handling of information sensitive to U.S. national defense.

"Mr. Assange said very clearly he believes there should be First Amendment protection for that conduct, but the fact of the matter is, as written, the Espionage Act does not have a defense for the First Amendment," Pollack said.

The WikiLeaks organization posted a statement to X saying that Assange was due to fly to his native Australia. The administration of Australian Prime Minister Anthony Albanese has pressed for Assange's return.

"Regardless of the views that people have about Mr. Assange's activities, the case has dragged on for too long. There's nothing to be gained by his continued incarceration, and we want him brought home to Australia. And we have engaged and advocated Australia's interests using all appropriate channels to support a positive outcome, and I've done that since very early on," Albanese said in Parliament on Tuesday.

In a breakneck denouement to a 12-year stalemate with the U.S., Assange left London's high-security Belmarsh Prison on Monday and boarded a Bombardier Global 6000 private jet for Saipan, with a brief layover in Bangkok for refueling. His wife, Stella Assange, wrote in a Tuesday social media post that he was not permitted to fly commercial airlines or routes to Saipan and onward to Australia. She also asked X users for donations to cover the cost of travel, which amounted to $520,000, she said.

Battle against extradition

The 52-year-old Assange has been battling extradition for more than a decade. In that time, Assange has spent seven years in self-exile in the Ecuadorian embassy in London and the last five years at Belmarsh.

Assange was wanted in the U.S. on 18 charges, including 17 under the Espionage Act and one under the Computer Fraud and Abuse Act. He faced up to 175 years in prison after WikiLeaks published hundreds of thousands of leaked confidential military files and diplomatic documents related to the Afghanistan and Iraq wars.

WikiLeaks gained international prominence in 2010 when the website released footage from a 2007 U.S. helicopter attack that killed two Reuters news staff and several others in Iraq's capital, Baghdad.

Following this high-profile release, WikiLeaks published hundreds of thousands of other classified files, making disclosures that often embarrassed Washington.

— CNBC's Sam Meredith contributed to this article.