"An individual who appears to be one of the main suspects of the twin attacks was arrested on the evening of June 10 as he tried to cross the (Syrian) border," the governor's office in the southeastern province of Hatay, where the bombs went off, said in a statement.
Local media have reported that the suspect, identified as NE, made dozens of trips between Turkey and Syria in recent weeks.
The attacks were the deadliest on Turkish soil since the start of the Syrian conflict more than two years ago, and raised fears of the growing regional impact of the crisis, which has already killed more than 94,000 people.
Ankara has blamed Turkish extremist groups backed by the Syrian government for the Reyhanli bloodshed, though Damascus has denied involvement.
The Turkish government is a vocal supporter of the Syrian rebels fighting to overthrow President Bashar al-Assad and has taken in some 400,000 Syrian refugees who have fled the violence at home.