But then, in late 2009, Harrison was an eager 27-year-old applying for an unpaid internship, a graduate of a prestigious boarding school with ambitions to become a journalist.

Harrison had no prior experience, but MacFadyen said he saw a spark that led him to bring her on board — a break that would set her on the path to meeting Assange and eventually bring her into the whistleblower Web site’s inner circle.

“It was an intelligent choice to send her” to Snowden, MacFadyen said. “She’s smart, determined and fully believes in the moral principle of shedding light. This is something she has strong feelings about.”

After being recommended by MacFadyen, Harrison began working with WikiLeaks in August 2010 on the internal vetting of confidential U.S. documents supplied by Army Pfc. Bradley Manning, which the site later released. At some point that year, according to two people with direct knowledge of the situation and who spoke on the condition of anonymity, Harrison and Assange became intimately involved. They cautioned that the relationship was not Harrison’s prime motivation in championing the WikiLeaks cause.

“She is firmly committed to what WikiLeaks is trying to do; she believes 100 percent in the mission,” one of the people said. “Any suggestion that her relationship with Julian is what has compelled her to do the things she has would be a totally wrong assumption.”

Although those who know her as an Assange confidante describe her as more comfortable behind the scenes, Harrison now finds herself in the spotlight. She has raced across continents to aid Snowden, assisting in his flight from Hong Kong and his search for asylum from Moscow. (On Friday, Venezuela offered Snowden asylum and Nicaragua said it would do so “if circumstances allow it.”) All the while, she has has maintained a low profile and refrained from public statements.

Acknowledgment of her role has come via bare-bones WikiLeaks statements and a comment from one Russian authority. Kristinn Hrafnsson, a WikiLeaks spokesman, declined to comment for this article. Harrison did not respond to an interview request. Assange, who has been holed up at Ecuador’s embassy in London for more than a year, said in an e-mailed statement that “Sarah is spirited, courageous and completely incorruptible,” but did not comment further.

Those who know Harrison say she appeared to blossom under Assange’s tutelage, going from starry-eyed intern to a savvy crusader for the no-holds-barred brand of public disclosure that has come to define WikiLeaks.

Harrison grew up in a privileged British home, her father a retail industry executive and her mother a specialist in treating reading disabilities. In a brief telephone interview, her father, Ian Harrison, 74, said he was not “going to make any further comments about our family and our private life,” citing bad experiences with the British tabloid press.

He referred to an interview the family had given to the Daily Mail, which produced an article last weekend headlined: “The public school girl who fell for Julian Assange — then went on the run with the world’s most wanted man.”

He said he had not spoken to his daughter since her involvement with the Snowden case became known and had been keeping up with her movements largely by following the news. “We are proud of our daughter,” he said. “We just hope she is well.” When asked how his daughter would describe her profession, he said: “I would have said investigative journalist would have summed her view of what she does.”

Still, Harrison’s role within WikiLeaks has taken many forms over the years. A short biography on the WikiLeaks Web site describes her as a member of the group’s “legal defence team.” But Harrison is not a lawyer and studied English while at Queen Mary, University of London.

MacFadyen called her a dogged researcher, one reason he recommended her in 2010 to work on WikiLeaks documents. He believed she was a perfect fit for the work being done by Assange, whom MacFadyen had first met in California in the late 2000s and had since come to know and trust.

By 2011, however, Harrison had risen through the WikiLeaks ranks, becoming what some describe as “Julian’s gatekeeper.” She stepped in for Assange to conduct at least one WikiLeaks news conference, coming off as good-natured and self-assured. In a conversation with two Washington Post reporters in February 2011 at the Frontline Club for journalists in London, Harrison, who was sitting with Assange at the time, appeared fiercely loyal, criticizing a media outlet she felt had betrayed his trust.

“She was at first in an incredibly vulnerable position, put in a job without any kind of mentoring, and then basically became Julian’s assistant,” said Heather Brooke, an American journalist who investigated WikiLeaks for her book “The Revolution Will Be Digitized.” “She is one of the cult of the faithful to Julian now, his gatekeeper, someone who ended up managing who did and didn’t get access.”

Harrison’s defenders describe her as technical-minded and a fierce advocate of information disclosure.

“Sarah is there not because of any relationship with Julian,” said Stefania Maurizi, a journalist with Italy’s l’Espresso magazine who has maintained weekly contact with Harrison over the past three years. “Sarah is there because of her skills; she is a very skilled person. She believes in what she is doing.”

Vaughan Smith — who gave Assange refuge inside his sprawling English estate, Ellingham Hall, for 17 months while he fought a Swedish extradition order — recalled Harrison as deeply involved not only in WikiLeaks-related tasks, but also as a researcher on Assange’s legal case. Assange was fighting a request by Swedish authorities to question him on sexual assault allegations, which he has called a politically motivated smear campaign. Harrison, Smith said, quickly became part of a small group of WikiLeaks lieutenants who regularly strategized his defense from inside Smith’s country home, which Assange left in June 2012 to seek asylum.

Smith said that during Assange’s long stay, Harrison was a peacemaker always able to smooth things over during tense moments. He said he applauded her dedication despite “meager pay and potential risk.”

“It’s not as if she’s getting anything out of this other than doing something that she believes is right, helping a whistleblower,” said Smith, who owns the Frontline Club. “What she’s done takes a certain amount of courage, especially for someone who never sought the spotlight. This will be difficult for her; she is not used to getting this kind of attention. But she is trusted by Assange, and she clearly wanted to help WikiLeaks help Snowden. Assange needed someone, and she volunteered.”