Mahir "Mike" Hawash, 39, said on Monday he regretted his actions.
"I wish to ask forgiveness from my family for the pain I have caused them, and to my friends, my friends in the community and in the United States," he said.
Mahir, a Palestinian Muslim from the West Bank, and two Muslim brothers from Oregon agreed to cooperate in a case in which six men were convicted of trying to link up with Taliban forces.
Hawash was held for weeks without charges after his arrest in March 2003, prompting supporters to stage rallies, write to officials and put up a website demanding he should be released or charged.
There were no crowds or demonstrations at Monday's sentencing, but several of his staunchest supporters submitted letters to the court attesting to his good character.
A letter from Mahir's wife Lisa called the event "an aberration in his otherwise good and generous life. I can look into his eyes and see the sadness and remorse. It is truly genuine".
Hawash, a US citizen for 15 years and apparently a model suburban dad, told the court he is proud to be an American, recalling his pride when he voted in his first election.
He attributed his crime to religious and emotional confusion in the highly charged times after the hijack attacks on the World Trade Center and Pentagon on September 11, but added, "I do not blame anybody but myself".
Judge Robert E Jones noted that one of his court officers was a US military pilot in Afghanistan when the group tried to enter the country.
The US accused the Taliban of
harbouring Usama Bin Ladin
"You might have killed my extern sitting right here," Jones said, "That is a very, very serious act."
Two other defendants - Ahmad Bilal, 25, and his brother Muhammad Bilal, 23 - received 10 and eight-year sentences respectively on Monday. They did not speak to the court.
Patrice Lumumba Ford and Jeffrey Leon Battle previously received 18-year sentences.
Battle's wife October Martinique Lewis stayed behind and wired the group money. She previously received a three-year sentence as part of a plea deal.
Meanwhile, a final suspect, Habis al-Saub, a Jordanian with US permanent resident status and the only foreigner in the group, remains at large.
Government officials believe al-Saub was later killed in Afghanistan.
The United States attacked Afghanistan to topple the Taliban government nearly one month after the 11 September 2001 attacks.
The Bush administration accused the Afghan government of harbouring Usama bin Ladin - the man it accused of masterminding the strikes.
Muslims around the world were incensed by America's attack on the Islamic nation, and many volunteered to defend Afghanistan against the assault.