George Livio was arrested in August 2014 because of his work and was not charged with any crime. UN officials feared he would be accused of treason, which they said carries the death penalty.
A government spokesman was not immediately available for comment today.
The UN says two other officials have been held without trial since 2014, but it did not give their names.
South Sudan has cracked down on media. Newspaper articles often appear with entire sections blank, evidence of national security censors.
South Sudan faces both civil war and famine.