The man arrested was identified as Imran Kassim, 34, with Singapore's Ministry of Home Affairs saying he had tried to make his way to Syria to join Islamic State fighters at least twice.
He had been prepared to attack members of the Singaporean armed forces, officials say, before he was arrested on Thursday along with a woman who was in contact with foreign militants.
"In February 2014, he travelled to Syria to oversee the delivery of humanitarian aid to a refugee camp that was arranged by the logistics company where he was a managing director," the ministry said in a statement.
"At the refugee camp, he had intended to slip away from his hosts and make his way to join ISIS, but was unsuccessful.
"In March 2015, Imran contacted a pro-ISIS foreign contact to facilitate his entry into Syria to join ISIS, but did not receive any reply."
More recently, Imran had intended to join militants who seized control of Marawi City in Philippines this year, the ministry said in a press release.
The ministry also alleges Imran took the pledge of allegiance to IS leader Abu Bakr al-Baghdadi.
Imran's arrest came as a result of information given to police by "people close to him".
Singapore, regarded as the most stable country in south-east Asia, has become increasingly concerned about the risks of radicalisation among its Muslim minority.
At least 14 radicalised Singaporeans have been put under restriction or detention orders under a tough internal security law since 2015, up sharply from 11 cases between 2007 and 2014, the government said in June.
Authorities have mounted a campaign to encourage family members, friends and neighbours to report on anyone they fear was in danger of becoming radicalised.
The woman who was arrested was identified as Shakirah Begam binte Abdul Wahab, a 23-year old administrative assistant. The ministry said she had been in contact with several foreign fighters since 2013.
She was put under a restriction order, which means suspects are monitored and their movements are restricted.
