Ali Alvi al-Hamidi admitted to conspiring to murder Americans abroad, conspiring to provide material support to Al-Qaeda and to receiving military-type training from the terror network.
He entered his plea before US District Judge Nicholas Garaufis in federal court in Brooklyn. He now faces spending the rest of his life behind bars.
US prosecutors said Hamidi went to Pakistan's northwestern tribal belt in early 2008 to join Al-Qaeda and learn how to use weapons, bombs and detonators.
Prosecutors said he helped US citizen Bryant Neal Vinas join Al-Qaeda.
Vinas traveled to Pakistan for Al-Qaeda training and was recruited into a plot to attack the Long Island Railroad, a commuter line that connects Manhattan to the suburbs on Long Island.
Vinas was arrested in 2008, before he could carry out the attack, and pleaded guilty to terror charges in 2009.
