I grew up in northern Massachusetts and then southern New Hampshire. I became interested in philosophy in 9th grade thanks to a world civilization teacher that insisted we cover intellectual history. I was fascinated by how ideas shaped world events. I started with Marx and Locke. Political philosophy was my first love. I've returned to it as one of my specialties, though I originally planned to specialize in philosophy of mind when I went to graduate school. I'm also interested in economics and using the tools of the social sciences to improve philosophical theorizing.

I was married to Lauren Oviatt Brennan in June 2004. Our son Aiden Alexander Brennan was born in November 2007.

My biggest hobby is music. I've played guitar since age 11 or so, and, accordingly, also play bass. I started playing drums, too, in 2008. My favorite genre is metal, especially progressive metal and "shred", but I also play classical, jazz, and blues. My main guitars are an Ernie Ball Music Man JP6 Limited Edition, a Fender Lonestar Stratocaster, and a Carvin DC400. I play through a Mesa Boogie Mark V amp.