Trained as an economist, Brennan collaborated extensively with Nobel Prize winner James M. Buchanan and became the first non-American president of the Public Choice Society in 2002.
Brennan published widely on rational actor theory, philosophy, and economics, and sat on the editorial board of the academic journal Representation.
[2] He held academic positions in several related departments at Australia National University and Virginia Tech.
With Loren Lomasky he won the American Philosophical Association's Gregory Kavka Prize in Political Philosophy for the paper "Is There a Duty to Vote?"
[5] Brennan was a golfer, and a semi-professional singer (for some years a national recitalist with the ABC).