Frankie Boyle is suing the Daily Mirror newspaper for libel, after they branded him "racist" in an article.
He says the story, published on July 19 2011, affected the talks he was having with Channel 4 to start up a new TV show.
The piece opened: "RACIST comedian Frankie Boyle could soon be returning to TV despite upsetting thousands of viewers."
The tabloid is unrepentant, saying it will back up its case with examples of Boyle's jokes over recent years.
It says it will defend itself "on the basis of truth and fair comment", according to BBC News.
The trial, taking place at the High Court in London, will apparently last a week.
Boyle's barrister David Sherborne claims his client was forced to quit Mock The Week over the allegations, adding that to label someone racist is "obviously defamatory".
"Saying 'vile' or 'offensive', or his material is 'vile' or 'offensive', is one thing," he told the jury. "He realises that that goes with the territory, so to speak. But accusing him of being a racist is an entirely different matter."
The Mirror has not removed the article in question from its website.