Thornton received a Bachelor of Arts in Latin from the University of California at Los Angeles in 1975. He received a PhD in Comparative Literature from the University of California at Los Angeles in 1983. He had studied Greek, Latin, and English literature for his doctorate.

Thornton is a frequent guest on talk radio shows across the United States. He has lectured at the Smithsonian Institution in Washington, D.C. He also appeared regularly on ABC's Politically Incorrect with Bill Maher. Thornton is a regular contributor to the conservative website CaliforniaRepublic.org as well.

He has written for numerous publications such as National Review Online, Heterodoxy, The National Herald, The Washington Times, The Los Angeles Times, Helios Magazine, Arion, The San Francisco Examiner, The American Enterprise, The University Bookman, Religious Studies Review, Intercollegiate Review, The American Journal of Philology, City Journal, and FrontPage Magazine. Thornton has also written several well received books.

Thornton has described his opinions as opposed to the dominant, mainstream historical tradition about the Enlightenment. He is an admirer of historian and author Christopher Dawson. He also subscribes to the 'Athens verses Jersualem' thesis of Leo Strauss, in which the interplay between classical Greek ideologies of rationality and the Judaeo-Christian spiritual philosophies resulted in the creation of Western civilization.

Thornton believes that the declining belief in interpersonal ideals such as national pride and in religious ideals such as Christianity has led non-American Westerners to either substitute "political religions" such as communism and fascism into their lives or abandon having moral ideals altogether. This, in his opinion, weakens them against pressure from threats such as increasing immigration to Europe by Muslims that have higher birth rates than native Europeans. He has said, "If all of their goods are material, right, what material good is worth dying for and what material good is worth killing for?"

Thornton is a strong critic of the Obama administration. He wrote in February 10, 2009:

So far, we have heard nothing from the Obama team that suggests they will be any more successful than previous administrations in thwarting the designs of our enemies. Instead, look for more talk, more summits, even more agreements that, in the end, will leave us weaker and our enemies stronger.