Mustafa Sultan Ali is the first Singaporean to be arrested abroad for trying to join ISIS, which has attracted some 30,000 foreign fighters to territory it controls in Syria and Iraq, including some 1,000 from Southeast Asia.
He also told Singapore authorities that he was prepared to carry out attacks in Singapore.
Mustafa, whose occupation was not disclosed, had left Singapore in late May this year for a neighbouring country.
He then boarded a flight to Turkey from there.
He took that travel route in the hope of hiding his tracks, the ministry said.
He had planned to cross into Syria from the Turkish border, but was detained by local authorities in Turkey and subsequently deported to Singapore in June 2015.
"Investigations showed that Mustafa had been deeply radicalised by the terrorist ideology of ISIS and other radical ideologues he had come across online," the statement added.
"He had travelled to Turkey and tried to make his way to Syria in order to participate in armed violence by fighting alongside ISIS.