He has a radio show that is the toast of conservative America and his extremist rants accusing President Barack Obama of being anti-white and a closet socialist have made him a star on Fox News. His speaking tours sell out like a rock star's and his published political diatribes are bestsellers.

Now Glenn Beck, loved by the right and loathed by the left, is promoting his anti-government conspiracy theories in a most unexpected branch of the arts: the novel. This week will see the publication of The Overton Window, Beck's near-future thriller that reads like a Tea Party activist's dark fantasy of brave patriots fighting for America against their own freedom-squashing government.

The protagonist and hero is Noah Gardner, a public relations executive who falls in love with a woman called Molly Ross. She gradually convinces him of the existence of a great threat to America which, as every Tea Party activist will instantly guess, has its source in the government. "An unprecedented attack on US soil shakes the country to the core and puts into motion a frightening plan, decades in the making, to transform America and demonise all those who stand in the way," reads the publisher's blurb. According to Beck himself, the book will feature a heroic citizens' group called the Founders Keepers, whose name sounds a lot like the Oath Keepers, a real-life conservative group of police officers and soldiers founded last year who believe their own government is a growing threat to freedom.

Since Obama's election a host of conspiracy theories have grown up on the extreme right of American politics. They range from Obama being a secret Muslim or communist to theories that the government intends to confiscate citizens' guns and round up dissidents into concentration camps. Beck is a hero to the movement.

Yet, despite the seeming outlandishness of its plot, Beck's thriller is almost guaranteed to be a massive bestseller. "Glenn Beck's fans are so devoted to following all his stuff that they are bound to go out and buy this book," said Carolyn Kellogg, a blogger on the Los Angeles Times book blog, Jacket Copy.

Judging by an audio excerpt of Beck's prose released last week, the book has no pretensions to the highbrow. Here is Beck introducing his hero: "He had spent a full decade building what most guys would call an outstanding record of success with the ladies. Good looking, great job… Noah had all the credentials for a killer eHarmony profile." Noah's love interest is described as "hot, but it was an aloof and effortless hotness that almost double-dared you to bring it up".

Some people see Beck's entry into the literary world as worrying. There is a long tradition of stirring political debate via fiction that ranges from literary greats like George Orwell's Nineteen Eighty-Four and Animal Farm to underground tracts like the racist Turner Diaries, which described a race war in America and inspired the Oklahoma bomber Timothy McVeigh. The Overton Window is playing directly to conservative fears of big government and the loss of US power and the nation's way of life. "This whole nuttiness that the government is this big, bad thing that is against the people is becoming more common. This book feeds that paranoia," said Professor Jim Corcoran, an expert on far-right groups in America at Simmons College, Boston.

The title of the book itself refers to a concept in political science that seems to have resonated with Beck. It was developed by Joseph Overton and describes a "window" of what ideas are deemed acceptable in any given society. By introducing other fringe ideas this "window" can be moved to the left or the right and once unacceptable concepts can become part of the mainstream.

Beck is already a huge influence on book sales. The "Beck bump" catapulted A Patriot's History of the United States into the number one spots on Amazon and the website of bookseller Barnes and Noble. He recently did the same for The Road to Serfdom, a book written in 1944 that most Americans had never heard of. Even books he dislikes get a huge sales boost. He recently mentioned an "evil" leftwing anarchist book called The Coming Insurrection. It promptly rocketed into the bestseller lists. The Overton Window will undoubtedly follow it there.