Kim Dong Chul, 62, was arrested in North Korea in October and had admitted to committing "unpardonable espionage" including stealing military secrets, the North's official KCNA news agency reported earlier.
Weeks earlier North Korea sentenced American Otto Warmbier to 15 years hard labor in March for trying to steal a propaganda banner.
State prosecutors had sought a 15-year sentence for Kim. His defense attorney requested leniency considering his age, KCNA said.
"The accused confessed to all crimes he had committed ... and gathered and offered information on its party, state and military affairs to the South Korean puppet regime, which are tantamount to state subversive plots and espionage," it said.
Kim was shown in photographs handcuffed and wearing a tie and blue jacket. He looked distressed and was flanked by guards.
North Korea, criticized over its human rights record for years, has used detained Americans in the past to extract high-profile visits from the United States, with which it has no formal diplomatic relations.
The U.S. State Department declined formal comment, citing privacy issues, but a State Department official, who did not want to be identified, said the United States was aware of media reports of the sentencing.
The official said that in cases where U.S. citizens were detained in North Korea, the United States worked with the Swedish Embassy in Pyongyang, which looks after U.S. consular affairs in North Korea, to ensure their welfare.
North Korea has previously handed down lengthy hard labor sentences to foreigners, though eventually freeing them before they served their full terms.
Six foreigners, including Kim and three South Koreans, are known to be detained in the North.
Kim, who has said he is a naturalized American citizen, had confessed to committing espionage under the direction of the U.S. and South Korean governments and apologized for his crimes, according to the North's KCNA news agency in March.
He told foreign media then that he was born in 1953 in Seoul and moved to the United States when he was 19. He said he set up a business in the North Korean special economic zone of Rason in 2008.
Kim said his two daughters lived in New York and he had siblings in South Korea, KCNA said in March.
North Korea has tightened security ahead of its first ruling party congress in 36 years, which will begin on May 6. It has also intensified its pursuit of nuclear weapons and ballistic missiles since its fourth nuclear test in January.