Viktor Bout, 42, was arrested in Bangkok in March last year during a sting operation led by U.S. agents. The United States accuses Bout of conspiring with others to sell millions of dollars' worth of weapons to the Revolutionary Armed Forces of Colombia (FARC).
Today's session will be dedicated to witness accounts, Russia's Vesti 24 television said. Bout's lawyers insist that the defendant was arrested in violation of Thai laws, and demand his immediate release from custody.
Bout recently said his case was fabricated by the U.S. authorities for political reasons.
"There was no evidence shown during the trial last year that would incriminate me on the charges. It is purely a political matter," Bout said.
"The Americans failed to present anything concrete other than questionable claims," he added.
A court in Bangkok announced last Monday its intention to close the hearings this month, setting the dates for March 17 and 18.
Bout, a former officer in the Russian army, faces a life sentence if extradited and tried in a U.S. court. However, Thai authorities earlier announced that they would not press charges against Bout.
Western law enforcement agencies consider Bout to be "the most prominent foreign businessman" involved in trafficking arms to UN-embargoed destinations, including the Democratic Republic of Congo and Angola.
UN reports say Bout set up a network of more than 50 cargo aircraft around the world to facilitate his arms shipments, earning him the nickname "merchant of death."
In an interview published in a Russian newspaper in October, Bout said Washington fabricated charges against him after he had refused to work as an informant.
