Siu received her Ph.D. from the Department of Communication at Stanford University, with a focus in political communication, deliberative democracy, and public opinion, and her B.A. degrees in Economics and Public Policy and M.A. degree in Political Science, also from Stanford.

Siu has advised policymakers and political leaders around the world, at various levels of government, including leaders in China, Brazil, and Argentina. Her research interests in deliberative democracy include what happens inside deliberation, such as examining the effects of socio-economic class in deliberation, the quality of deliberation, and the quality of arguments in deliberation.