Joseph Hassan Farrokh, 28, of Woodbridge, admitted Friday in a federal court in Alexandria.
He was one of two men charged with terror-related offenses in January after trying to travel to Syria.
The second man, Mahmoud Amin Mohamed Elhassan, 25, is accused of aiding and abetting his efforts.
Farrokh was charged in January and faces a maximum penalty of 20 years in prison when sentenced on July 15.
Prosecutors said Farrokh had been trying to join ISIS since at least November. He met with someone Elhassan “believed maintained connections to individuals engaged in jihad overseas,” the Justice Department said in a statement.
In January, Elhassan drove Farrokh to Richmond, where Farrokh went to the airport and cleared security in a bid to board a Chicago-bound flight, prosecutors said. From there, authorities say, he planned to fly to Jordan and eventually travel to Syria to join ISIS.
Authorities arrested him at the airport. Elhassan was arrested after returning to Woodbridge, Virginia, where the two lived.
The FBI estimated in October that 250 U.S. residents have traveled or tried to travel to Syria to fight in the civil war raging there.