Mohammad Hassan Khalid sentenced to five years in prison after pleading guilty to taking part in a plan to kill a Swedish artist.
Khalid, 20, is the youngest person ever convicted of US terror charges.
Khalid has been in custody for three years for his role in the "Jihad Jane" conspiracy, will receive credit for that time and serve an additional two years in prison to finish his sentence, said the sentencing judge, Petrese Tucker.
Dressed in a baggy green prison jumpsuit, Khalid begged the judge for mercy and thanked his parents for their support during a court appearance.
"Mom, Dad, you will forgive me 1,000 times even though I don't ask for it," said Khalid, who pleaded guilty to committing related crimes when he was as young as 15 and living in his parents' apartment in suburban Maryland.
He was arrested in 2011 on charges he provided material support to terrorists working with a suburban Philadelphia housewife who went by the nickname Jihad Jane. Her real name is Colleen LaRose.
LaRose was sentenced to 10 years in prison in January for planning to murder artist Lars Vilks, who had depicted the head of the Muslim Prophet Mohammad on a dog.
Prosecutors had asked for a stiff sentence for Khalid, arguing that his translations of extremist propaganda helped explain violent ideologies to potential recruits on the Internet.
Khalid had faced up to 15 years in prison but prosecutors asked for a shorter sentence because he cooperated after his arrest.
His lawyer called the case overblown and described his client as an awkward, isolated and vulnerable boy who has since been diagnosed with Asperger's Syndrome, a form of autism characterized by repetitive behavior, a need for rules and routines, and problems with social interaction.
LaRose admitted to following orders in 2009 from alleged al-Qaeda operatives. She traveled to Ireland that Autumn to meet an Algerian, Ali Damache, who she believed would train her.
The plot was not carried out and Mr Damache is fighting extradition to the United States on terror charges. Prosecutors said Khalid helped Mr Damache recruit others and helped LaRose destroy evidence.
Officials said Khalid "worked tirelessly" with two other American men now serving long prison terms on terror charges inother failed plots, Emerson Begolly and Reed Stanley Berry. Prosecutors say he helped them translate violent jihad videos from Urdu to English.
Prosecutors also cited online postings in which Khalid tried to raise money for terrorists, but there is no public evidence that anyone ever sent him any money.