Following a tip-off from another country, which was not identified, Greek authorities traced the 34-year-old suspect in Athens.
The detainee is being held and interrogated by the anti-terrorist service, while a search followed at the house where he had been staying.
The arrested person had arrived in Greece, with an initial stop on the island of Lesbos (Lesvos), in 2017. He is married and is the father of four children.
During his stay in the country, he had twice applied for political asylum, but on both occasions his application had been rejected.
He had recently appealed to the administrative courts against the court decisions, citing humanitarian reasons.
Greek authorities reportedly knew of his presence in the country, but information from a foreign intelligence service that informed Greek authorities that the Iraqi had been an ISIS operative accelerated developments leading to his arrest.
A video posted on the internet depicts the suspect preaching terrorism.
The 34-year-old was located in the center of Athens where he lived with his family. He is expected to appear before a prosecutor on Tuesday.
Several ISIS members arrested in Greece
Greece has arrested a number of ISIS members in recent years, as extremists have taken advantage of the migrant influx to Greece.
In November 2020, a 27-year-old Syrian man was jailed after he was charged with two crimes linked to ISIS terror attacks.
The suspect had originally confessed to police that he was indeed an ISIS member and pointed himself out in a video recording of ISIS fighters murdering civilians in 2014.
In testimony before the magistrate, however, he recanted and denied all the charges, claiming that the confession had been extracted by the use of torture.
The charges against the 27-year-old, who was residing at the Eleonas refugee and migrant housing facility in Attica, are for participation in a terror organization and direct involvement in murder as an act of terror.
In 2018, a 33-year-old Syrian national had been convicted on murder and explosives charges related to his participation with ISIS.
Earlier in the same year, an Afghan national caught carrying dozens of detonators was detained in Athens by Greek police and charged with the illegal possession of explosives.
In May 2017, a court in Komotini, northern Greece also convicted two members of the Islamic State terror group and sentenced them to 15 years’ imprisonment for unlawful arms possession.
The two men — a 30-year-old Swedish national and a 21-year-old Yemeni — were carrying hunting knives and were trying to cross into Turkey.