Aymen Sabawi, described by US authorities as a regime insider and supporter of the anti-US fighters, was convicted on Monday.
The charge came out of Sabawi's trial in September for possession of illegal weapons and bomb making, when he referred to his travels across the frontier.
He was sentenced to six years in prison then.
Sabawi was captured last May near Saddam's hometown of Tikrit by US and Iraqi forces.
His father, one of Saddam's half brothers, is also in custody awaiting trial.
According to the US military on Tuesday, Sabawi and his family were active in financing and supplying weapons to the ongoing fighting.
The conviction comes as Saddam himself, along with seven of his deputies, is on trial for massacring Shia villagers in Dujail in 1982.