Julian Assange, the WikiLeaks founder who has long fought extradition from Britain to the United States, agreed on Monday to plead guilty to one count of violating the Espionage Act in exchange for a five-year prison sentence.

Under the agreement he will be freed, having already served that time while in British custody. The deal brought an abrupt end to an extraordinary legal saga that has raised novel issues of national security, press freedoms, politics and diplomacy.