Ali Yumakci, of Northumberland Park, was arrested as part of an investigation into online terrorist material.
The 21-year-old was stopped at the airport on June 23, 2023, and phone analysis revealed he had sent a number of pro-Daesh videos and materials to a WhatsApp group were assessed by officers.
He was charged with three counts of breaching section 2 of the Terrorism Act 2006.
Yumakci was convicted of two counts of disseminating terrorist material after a one-week trial at the Old Bailey.
He will be sentenced at the same court on November 28.
Commander Dominic Murphy, who leads the Met’s Counter Terrorism Command, said: “Schedule 7 stops, which allow police to question, search and detain people at ports, can be vital in securing evidence against those involved in terrorism offences.
“Analysis of the mobile phone seized from Ali Yumakci at Heathrow revealed he had been disseminating terrorist material.
“There is no place for hateful, terrorist ideology to be spread online and where we identify people who we believe to be committing offences, we will investigate and take action.”
