Farooque Ahmed of Ashburn was sentenced to 23 years in prison Monday immediately after entering his guilty plea as part of a deal with federal prosecutors.
Ahmed, a naturalized citizen from Pakistan, apologized in court for his conduct.
He pleaded guilty to conspiring to provide material support to al-Qaida and collecting information for a terrorist attack on a transit facility.
Authorities say Ahmed plotted with people who turned out to be part of a six-month government sting. He allegedly took video of Northern Virginia subway stations and suggested ways a bomb could inflict the highest number of casualties.