WikiLeaks once again seized the global spotlight on Sunday by assisting Edward J. Snowden in his daring flight from Hong Kong, mounting a bold defense of the culture of national security disclosures that it has championed and that has bedeviled the United States and other governments.

Accompanying Mr. Snowden on the Aeroflot airliner that carried him on Sunday from Hong Kong to Moscow — continuing a global cat-and-mouse chase that might have been borrowed from a Hollywood screenplay — was a British WikiLeaks activist, Sarah Harrison. The group’s founder, Julian Assange, who has been given refuge for the last year in Ecuador’s embassy in London, met last week with Ecuador’s foreign minister to support Mr. Snowden’s asylum request. And Baltasar Gárzon, the legal director of WikiLeaks and a former Spanish judge, is leading a volunteer legal team advising him on how to stay out of an American prison.

“Mr. Snowden requested our expertise and assistance,” Mr. Assange said in a telephone interview from London on Sunday night. “We’ve been involved in very similar legal and diplomatic and geopolitical struggles to preserve the organization and its ability to publish.”

By Mr. Assange’s account, the group helped obtain and deliver a special refugee travel document to Mr. Snowden in Hong Kong that, with his American passport revoked, may now be crucial in his bid to travel onward from Moscow.