<p align="justify">Marriage equality or the equal status of same-sex marriage has undergone a rather tough road in Australia, involving diverging opinions in parties at the state and federal levels and constitutional amendments. It appears that people in power set the agenda on the legalization of same-sex marriage. However, it cannot be denied that social media played an almost decisive role in this process because it enabled the gathering of massive public opinion to pressure the government to make changes. To be specific, social media or social networking sites offered platforms for people concerned to share reports about the progress of foreign countries in legalizing same-sex marriage, to express their opinions and to launch campaigns in support of their beliefs. This essay explores the role that social media played in the legalization of marriage equality movement in Australia from the perspectives of the public sphere theory and the agenda-setting theory.</p>