Specialist Ryan Anderson, 26, "was found guilty on all charges" on Thursday. A convert to Islam, he was reported to have attempted to make contact with al-Qaida through internet chat rooms in May 2002.
He was nabbed by Shannen Rossmiller, a municipal judge from Montana, who in her spare time sought to "catch terrorists on the internet".
Judge Rossmiller told prosecutors that while she was monitoring a website devoted to hardline Muslims she came across an email posting from one "Amid Abd al-Rashid" - which turned out to be Anderson.
Rossmiller, masquerading as a hardline Muslim, began to correspond with Anderson. When she found out that he was a soldier, she contacted the Federal Bureau of Investigation.
Judge Debra Boudreau ordered a closed-door hearing on Andreson at the Fort Lewis army base, in southern Washington. The military decided not to seek the death penalty.
Three army intelligence officials testified on Tuesday: Rene Gonzalez, John Roee and Christopher Wallace. Gonzalez and Roee spoke about surveillance, and Wallace spoke about the al-Qaida network, Costello said.
Army officers Burt Whitlow and Ricardo Romero testified on Monday that they presented themselves as al-Qaida members to confirm Anderson's leanings, and set up a meeting at a book store in February.
At the meeting Anderson handed them his passport photograph, a computer diskette and other material.
Anderson was arrested after a second meeting, just weeks before his unit was scheduled to deploy to Iraq.