Bout, 45, was busted in a 2008 sting operation in Thailand, where undercover informants posed as members of the FARC, which the United States regards as a terrorist organization bent on killing Americans.
The Russian citizen was later extradited to New York, where a U.S. District Court jury in November convicted him on all four counts of conspiracy. He denied the allegations and his lawyer, Albert Dayan, told jurors that Bout was an honest businessman who had only attempted to sell two old cargo airplanes for $5 million.
Bout also was ordered to forfeit $15 million by Judge Shira Scheindlin on Thursday.
The judge denied federal prosecutors the life sentence they had sought for Bout, whose tale inspired the 2005 movie Lord of War starring Nicolas Cage.
The 25-year term for conspiring to acquire and use anti-aircraft missiles was made concurrent with similar prison sentences on charges of conspiring to kill U.S. citizens and officers, and providing support for a terrorist group.
At one point during his sentencing, when a prosecutor said Bout had agreed to sell arms to kill Americans, the Russian-speaking defendant shouted, through a translator, It's a lie! Bout told Scheindlin: I never intended to kill anyone. I never intended to sell any arms to anyone. He added, God knows this truth.
Prosecutors said the phony FARC deal with undercover informants working for the U.S. Drug Enforcement Administration involved 800 surface-to-air missiles, 30,000 AK-47 assault rifles, five tons of C-4 explosive and 10 million rounds of ammunition -- artillery worth millions of dollars that would be the envy of some small countries, U.S. Attorney Preet Bharara said after the jury verdict last fall.
After Thursday's sentencing, Bharara said: Viktor Bout has been international arms trafficking enemy number one for many years, arming some of the most violent conflicts around the globe. He was finally brought to justice in an American court for agreeing to provide a staggering number of military-grade weapons to an avowed terrorist organization committed to killing Americans. Today's sentence is a fitting coda for this career arms trafficker of the most dangerous order.
Before Bout became ensnared in the sting, he had been a notorious and prolific arms dealer since the 1990s. His weapons -- allegedly transported via his aircraft fleet -- have been sold in conflict zones such as Liberia, the Democratic Republic of Congo, Sierra Leone and Afghanistan.
The United Nations froze Bout's assets because he had backed the brutal regime of Liberian leader Charles Taylor. Bout's support was an effort to gain illicit access to diamonds, the U.N. alleges.
His life in the illegal-arms trade was detailed in the book Merchant of Death, published two years after the Lord of War movie.
In a telephone interview from his jail cell with the government-run Voice of Russia, published Wednesday, Bout said he was a trophy for DEA agents. He maintained his innocence while awaiting the possibility of life in prison.
Look, even an agent in the first arrest stopped to say, 'Oh, we saw the movie about you, we are so excited, let us take a picture with you,' Bout said. It's like a trophy for them; I am like a hunted deer whom they killed and now they want to take a picture, like I'm some wild animal and now they caught me and they're going to put me in their kitchen and show their kids and their grandkids and say, 'Oh, we hunted that animal.'