As a student, Allen was majoring in history at Stanford University and studied at California State University, Long Beach. He was a prominent member of the John Birch Society, of which he was a spokesman. He contributed to magazines such as Conservative Digest and American Opinion since 1964. He also was the speech writer for George Wallace during the Alabama Governor Presidential campaigns and was adviser to the conservative Texas millionaire Nelson Bunker Hunt.

Allen was the father of four children, including Mike Allen, the political news journalist who, as a Politico reporter, writes in a less editorialised manner than his father .

Allen died in 1986, at the age of 50 of a liver ailment.

In 1972, Allen wrote with Larry Abraham None Dare Call It Conspiracy (prefaced by John G. Schmitz), a best seller. It is said to have sold over five million copies worldwide during the United States presidential election. An investigator of US financial, industrial, and political elites, he wrote other books about the Council on Foreign Relations and the Trilateral Commission, claiming that the term "New World Order" was used by a secretive elite dedicated to the destruction of all national sovereignties. Allen's last book, Say "No!" to the new world order, was published posthumously in January of 1987.

Investigative reporter Chip Berlet argues that Allen's work provides an example of a synthesis of right-wing populism and conspiracism known as producerism.