He is a researcher in democratic theory and political philosophy and his lines of research focus on the study of deliberative democracy, participatory and digital democracy as well as new technologies at the service of citizen participation.

He currently leads the multidisciplinary research project Global Democracy Project, which studies the forms of democratisation of international institutions and the development of legitimate spaces of global governance. He also leads the research group participating in the European H2020 REDEM project and collaborates with New York University's GovLab on the CrowdLaw Project. 

He has published books such as La república deliberativa (Marcial Pons, 2006), Deliberative Democracy and Its Discontents, co-edited with Samantha Besson (Ashgate, 2006), Legal Republicanism (Oxford University Press, 2009), and A Political Philosophy in Public Life. Civic Republicanism in Zapatero's Spain, co-authored with philosopher Philip Pettit (Princeton University Press, 2010). Martí has been a Laurance Rockefeller Fellow at Princeton University (2008-2009) and a visiting professor at the University of Richmond (2014).