Trevor Reed, a student at the University of North Texas, said he could not remember the events of last summer because he was drunk when he was detained after leaving a party in Moscow.
But he denied the charge in court after hearing what he said was the flimsy evidence presented during the trial and the investigation's failure to obtain video evidence that could prove his innocence.
"It's clearly political," he told reporters in court.
The conviction is likely to spur media speculation that Reed could become part of a possible prisoner swap reportedly being negotiated by Moscow and Washington. Neither side has confirmed such talks are taking place.
Russia convicted US citizen Paul Whelan, also a former Marine, last month of espionage and sentenced him to 16 years in jail. Whelan denied wrongdoing. US investor Michael Calvey is being held under house arrest on fraud charges he denies.
Whelan's lawyer has said he believes Moscow wants to exchange Whelan for an arms dealer, Viktor Bout, and another Russian held in US prisons.
Prosecutors accused Reed of grabbing a police officer who was behind the wheel of a car after the American was detained on Aug. 15. That, they said, caused the vehicle to swerve dangerously. He was also accused of elbowing a second officer.
Reed said he traveled to Moscow in May last year to learn Russian and see his Russian girlfriend. She burst into tears in court and was escorted outside after swearing loudly during the verdict.
"This conviction, and a sentence of nine years, for an alleged crime that so obviously did not occur, is ridiculous," said John Sullivan, the US ambassador to Moscow. "This was theater of the absurd."
Reed's father, Joey, said he planned to appeal publicly to President Vladimir Putin to intervene in the case."We believe (this case) happened for one reason – he stumbled him into police custody because he was intoxicated, and once they saw they had a former US Marine they said 'We're gonna keep this guy'," he said.