HarperCollins secures Agatha Christie publishing rights

It is almost 85 years since the relationship between Agatha Christie and Collins publishers began with The Murder of Roger Ackroyd, one of the author's earliest and most famous works.

Now, 34 years after the undisputed queen of crime fiction died, the company – in its current guise as HarperCollins – has finally secured a deal to become her global publisher. The seven-figure agreement was signed yesterday – on what would have been Christie's 120th birthday – giving the company the right to publish printed works in English as well as digital and audio versions.

The author's 80 novels and short story collections have never fallen out of print since her death in 1976, an event which was marked by the dimming of lights in London's West End theatres. Her works still sell a million copies a year, according to HarperCollins.

Christie's grandson Matthew Prichard, chairman of Agatha Christie Ltd, said he and his family were "delighted", adding that Christie herself "valued her relationship with Collins enormously".

David Brawn, HarperCollins' publishing director, added that there was a bond between his company and its most famous author because of the length of time they had been working together. "Indeed, when she died, it was Sir William Collins who gave the address at her funeral," he said.

In 1976, Sir William recalled being sent to see Christie on an awkward errand. "The blurb of her new detective novel gave away a vital clue, and my uncle sent me to break the terrible news," he said.

"I was received with the greatest kindness, but little did I think that this was the beginning of a long and very special personal friendship with one of the most wonderful and modest people I have ever met."

The British novelist, most famous for her characters Hercule Poirot and Miss Marple, has sold more than two billion books worldwide, a feat exceeded only by William Shakespeare and the Bible. It is believed that she became a writer after her sister Madge challenged her to write a detective story.

Brian Murray, the chief executive of HarperCollins Worldwide, said that the last 10 years had seen global sales of Christie's work double and her popularity in foreign markets soar, especially in India, where she is now among the top 10 English language authors.