Arthur Jones, a Holocaust denier described as a Nazi by the Illinois Republican Party, is poised to win the Republican primary in the state’s Third Congressional District. He is running unopposed, all but guaranteeing he will soon be the official Republican candidate for the House of Representatives.

“There’s no way in the world they can knock me off the ballot,” said Mr. Jones, 70, who has unsuccessfully sought the nomination five times. His campaign website has a section devoted to conspiracy theories about the Holocaust, which he called “nothing more than an international extortion racket.”

The Republican primary in the district, a Democratic stronghold that includes part of Chicago and its southwestern suburbs, is on March 20. A spokesman for the Illinois Republican Party said it had difficulty recruiting anyone to run against Mr. Jones because “it is a very Democratic district.”

The final deadline for certifying primary candidates passed last month, but the spokesman said the party would consider lending its support to an independent or write-in candidate. That deadline is in June, according to the State Board of Elections.