[1] Machan was a syndicated and freelance columnist; author of more than one hundred scholarly papers and more than forty books, among them Why is Everyone Else Wrong?

[7] In 1970, with Robert W. Poole, Jr. and Manuel Klausner, he purchased Reason magazine, which has since become the leading libertarian periodical in America.

He was a visiting professor at the United States Military Academy at West Point in 1992–1993 and taught at universities in California, New York, Switzerland, and Alabama.

Machan wrote a memoir, The Man Without a Hobby: Adventures of a Gregarious Egoist (Hamilton Books, 2004; 2nd edition 2012).

His main focus was to challenge the conception of human knowledge whereby to know that P amounts to having reached a final, perfect, timeless, and finished understanding of P. Instead, Machan developed Ayn Rand's contextual conception of human knowledge (from Rand's Introduction to Objectivist Epistemology), but also draws on the insights of J. L. Austin, from his paper "Other Minds", and Gilbert Harman, from his book Thought, in works such as Objectivity (Ashgate, 2004).

(1991)[10] and in his book Putting Humans First: Why We Are Nature's Favorite (2004), but he also wrote on the ethics of animal treatment in the same work.

He was also a skeptic as to whether governments are able to help with global warming and whether human beings have made significant contributions to climate change.

On 1 May 2011, Machan was featured in a three-hour interview on C-Span 2's In Depth program as its selection of an author from the Western United States of America.