Brennan escreve sobre a teoria democrática, ética do voto, competência e poder, liberdade e fundamentos morais da sociedade do comércio. Ele foi chamado de "um dos maiores especialistas acadêmicos do mundo em votação e conhecimento político".[3]
Seu trabalho centra-se na intersecção entre a filosofia política normativa e as ciências sociais empíricas, especialmente em questões sobre o comportamento dos eleitores, patologias da democracia e as consequências da liberdade. Ele argumenta que a maioria dos cidadãos tem a obrigação moral de não votar.
2016 "When May We Kill Government Agents?: In Defense of Moral Parity," Social Philosophy and Policy.
2016 "Why Consequences Matter More: The Expressivist Objection to Privatization," Criminal Law and Philosophy.
2016 "A Libertarian Case for Mandatory Vaccination," Journal of Medical Ethics
2016 "Estimating the Cost of Adjunct Justice: A Case Study in University Business Ethics," Journal of Business Ethics
2015 "Markets without Symbolic Limits," Ethics.
2015 "Community, Diversity, and Equality in G. A. Cohen's Socialist Utopia," Analyse & Kritik. (Invited paper.)
2015 "Market Architecture: It's the How, Not the What," Georgetown Journal of Law and Public Policy 15.
2014 "How Smart is Democracy? You Can't Answer that A Priori," Critical Review 26: 4–30.
2013 "Is Market Society Intrinsically Repugnant?" The Journal of Business Ethics 112:271–81.
2013 "The Right to Good Faith: How Crony Capitalism Delegitimizes the Administrative State," Georgetown Journal of Law and Public Policy 11: 313–34.
2012 "Political Liberty: Who Needs It?" Social Philosophy and Policy 29: 1–27. Reprinted in Matt Zwolinski, ed., Arguing about Political Philosophy (London: Routledge, 2014)
2012 "Why Liberal States Must Accommodate Tax Resistors," Public Affairs Quarterly 26: 141–60.
2012 "For-Profit Business as Civic Virtue," The Journal of Business Ethics 106: 313–24.
2011 "The Right to a Competent Electorate'" Philosophical Quarterly 61, 700–24. Reprinted in Tom Lansford, ed., Opposing Viewpoints: Voting Rights (New York: Gale/Cengage2, 2015).
2011 "Condorcet's Jury Theorem and the Optimum Number of Voters." Politics 31:2, 55–62.
2010 "Scepticism about Philosophy." Ratio 23: 1–16.
2009 "Polluting the Polls: When Citizens Should Not Vote." Australasian Journal of Philosophy 87:4, 535–49.
2009 "Tuck on the Rationality of Voting." Journal of Ethics and Social Philosophy 3: 1–5.
2008 "Beyond the Bottom Line: The Theoretical Goals of Moral Theorizing." Oxford Journal of Legal Studies 28: 277–96.
2008 "What if Kant Had Had a Cognitive Theory of the Emotions?" In Valerio Rohden, et al. (eds.), Recht und Freiden in der Philosophie Kants: Atken des X. Internationalen Kants-Kongresses (Berlin: De Gruyter), 219–28.
2007 "Modesty without Illusion." Philosophy and Phenomenological Research 75: 111–28.
2007 "Free Will in the Block Universe." Philosophia 35: 207–17.
2007 "Rawls's Paradox." Constitutional Political Economy 18: 287–99.
2005 "Choice and Excellence: A Defense of Millian Individualism." Social Theory and Practice 31: 483–98.
2004 "Illiberal Liberals." Review Journal of Political Philosophy 2: 59–103. Translated into Turkish and reprinted in Liberal Düsünce [The Journal of Liberal Thought] 15 (2010), 61–89.