Ulugbek Kodirov, 22, had faced up to 30 years in prison.
Defence lawyer Lance Bell argued that Kodirov had accepted responsibility for his actions and was trying to straighten out his life. He said Kodirov wasn't a "big, bad terrorist".
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"I'm not calling him a victim, but he's a victim, to a degree, of social media," Bell said.
Kodirov pleaded guilty in February to threatening to kill Obama, providing material support to terrorism and unlawfully possessing a firearm. He said he came up with the plan to kill the president as he campaigned for re-election after communicating online with a man
he believed to be a member of an Uzbek Islamic group the United States classifies as a terrorist organisation.
Assistant US Attorney Michael Whisonant said Kodirov would have tried to kill Obama, and a foreign group would have taken credit, if he had not been arrested a year ago.
"This case is an example of how our youth can be radicalised by the propaganda and lies on the internet," Whisonant told the judge.
With limited proficiency in English, Kodirov worked seven days a week in a kiosk at a shopping mall in Alabama before his arrest, the defence said.
A complaint said Kodirov contacted an unidentified person trying to buy weapons in early July 2011, and that person became a confidential source for the government. Accompanied by the witness, Kodirov bought an automatic rifle from an undercover agent and made a final threat against the president, authorities said.
Authorities said Kodirov was in the country illegally because he obtained a student visa but never enrolled in school. He faces deportation after his release from prison.
