The 51-year-old, 20-year Army veteran cried as he apologized for his crimes.
Showing some leniency, the judge credited Hunter for an honorable military career that led to numerous commendations. But she said his "grave and serious" crimes warranted stern punishment.
Hunter was brought to the United States in 2013 to face conspiracy charges. Prosecutors say he led two other ex-soldiers an American and a German in an USD 800,000 plot to kill the agent in Liberia.