Michael Baigent

Michael Baigent, who has died aged 65 of a brain haemorrhage, was a writer who gained international attention when he launched a court case claiming that The Da Vinci Code, the bestseller by Dan Brown, stole ideas from his own book.

The Holy Blood and the Holy Grail, which Baigent co-wrote with Richard Leigh and Henry Lincoln in the 1980s, is a book labelled non-fiction, but sometimes appeared on fiction lists (it was a bestseller in the New York Times fiction list). It explores the theory that Jesus married Mary Magdalene and suggests the couple had a child whose bloodline survives into the modern day.

In 2006 Baigent and Leigh made international headlines when they sued Dan Brown's publisher for copyright infringement, claiming that Brown appropriated what they described as the architecture of their book. Brown had to fly to London to be cross-examined in court, but a judge eventually ruled against Baigent and Leigh.

Born in New Zealand, Baigent grew up in the city of Nelson on South Island. He studied religion and psychology at the University of Canterbury in New Zealand before becoming a commercial photographer in various countries for several years, then moving to England in the 1970s. It was there he became interested in the Knights Templar and began researching the subject.

He met Leigh, an American novelist, and Henry Lincoln, a television scriptwriter, and together they worked on The Holy Blood and the Holy Grail.

Baigent was strident in his defence of the book: "Whole new generations of readers are discovering it, I have to say that it surprised us by maintaining its appeal and relevance. We would have expected some other work to take over where we left off. But this hasn't happened.

"Furthermore, much research has been undertaken during this time but The Holy Blood and the Holy Grail retains its solid position: there has been nothing discovered which oppose its basic themes and much discovered which support them."

The book (ironically published by Random House, which also published The Da Vinci Code) was moderately successful although the court case considerably boosted sales.

Baigent and Leigh collaborated on a number of follow-up books. They included The Messianic Legacy in 1986, which explored many of the same themes as Holy Blood.

There was also 1989's The Temple and the Lodge, a history of the freemason movement, and 1991's Dead Sea Scrolls Deception which suggested the Catholic Church had conspired to hide the scrolls. The pair's work also included a book about the Von Stauffenberg plot to kill Hitler.

Baigent also wrote a number of books without Leigh, the most recent of which was Racing Towards Armageddon in 2009.

The 2006 court case was a disaster for Baigent and Leigh, who died in 2007. Although Dan Brown admitted reading and drawing from it – indeed, he created a character that was a tribute to Baigent and Leigh – the judge ruled that, although there were similarities between the books, the parallels did not violate copyright and that there was nothing to prevent a novelist drawing on the research of a non-fiction writer. Baigent and Leigh were ordered to pay millions in legal fees.

Baigent is survived by his wife, Jane, two daughters, Isabelle and Tansy Baigent, a stepson, David, and a stepdaughter, Emma.