He is the host and producer of 99% Invisible, a KALW radio show and podcast, and a founder of the podcast collective Radiotopia, which he describes as efforts '"to broaden the radio landscape [and] make shows that aren't bound by [the] conventions" of public radio in the United States.He has also contributed to radio programs such as Radiolab and Planet Money.
Fast Company identified him as one of the hundred most creative people of 2013.
In 2004, he produced a program called Invisible Ink on KALW.
In June 2017, Mars launched the podcast What Trump Can Teach Us About Con Law with Elizabeth Joh, a professor of constitutional law at University of California, Davis, School of Law.