Lisa Smith has been arrested on suspicion of terrorist offences.
The 38-year-old former Irish Defence Forces member and her 2-year-old daughter were on board a Turkish Airlines commercial flight that landed at Dublin airport shortly after 10am.
In recent weeks, she was taken into Turkish custody following the bombing of a displacement camp in the north of the country.
Ms Smith is now being detained at a South Dublin garda station.
She will be questioned about her decision to travel to Syria to join the Islamic State in 2015.
Her daughter is now being cared for by relatives.
Speaking yesterday, Taoiseach Leo Varadkar said: "The gardaí are going to want to speak to her.
"They may be in a position to charge her and if they do, then prosecution may follow."