He is a professor of economics and finance at the University of Western Sydney, Australia. Keynesian-Marxist in training, he has worked in recent years to mathematically model Hyman Minsky's premonitory insights into the dynamics of current financial capitalism. Academically he has focused on lacking an empirical basis for criticizing the neoclassical interpretation of macroeconomics, Keen is influenced by economists such as Hyman Minsky, Irving Fisher, John Maynard Keynes, Piero Sraffa, Joseph Alois Schumpeter and Francois Quesnay.

Keen predicted the financial crisis in December 2005, and had warned as early as 1995 that a period of apparent stability could be no more than "the calm that precedes the storm." His prominent role as a member of a small minority of economists who foresaw the crisis and warned of its imminence was recognized by his peers with the Revere Award from the Real-World Economics Review, for being the economist who most strongly warned of the crisis, and whose work has a better chance of preventing similar crises in the future.