James Ujaama, 38, pleaded guilty last April to one count of conspiring to provide cash, computers and fighters to the now ousted Taliban regime, after being arrested in 2002.
In addition to the two-year jail sentence, US District Judge Barbara Rothstein sentenced Ujaama to three years of supervised release.
Born James Earnest Thompson in Denver, Colorado, Ujaama converted to Islam in the early 1990s.
In the late 1990s, he spent time in London where he met the radical cleric Abu Hamza, suspected by US of being an al-Qaida recruiting agent in Europe.
Abu Hamza has denied involvement in any terrorist activity.
Ujaama admitted in court that he "urged others to donate money, goods and services to Taliban-sponsored programmes and to charitable programmes in the territory of Afghanistan controlled by the Taliban."