The Singapore Police has arrested a Hizb ut-Tahir member named Zulfikar Mohamad Shariff (44) for spreading radical Islamist ideology online and radicalising at least two other citizens.
Hizb ut-Tahir is an international militant group banned in Bangladesh.
Zulfikar was arrested this month and ordered two years' detention, reports the Dhaka Tribune.
He made numerous Facebook posts that promoted and glorified terror group the Islamic State in Iraq and Syria (ISIS) or Daesh and its violent actions.
His postings contributed to the radicalisation of at least two other Singaporeans.
He first came under the spotlight in 2002 as head of the fringe group Fateha and for challenging mainstream Muslim leaders and agitating for primary schoolgirls to be allowed to wear the headscarf in schools there.
He also hosted politicians from Malaysia's Parti Islam SeMalaysia and went to Malaysia to speak on the issue and draw international attention to it.
He later became a research fellow with Monash University, and led an organisation called the Association for Democracy in Singapore that purported to push for free speech.
He resettled his family in Australia in 2002, and continued to pursue extremism by joining Hizb ut-Tahrir.
He also established and maintained contact with radical preachers such as Australia's Musa Cerantonio, who has inspired foreigners to fight in Syria, and radical British cleric Anjem Choudary.