During the 1970s Richard Leigh moved to the UK, where he met Michael Baigent, the man who was to be his flatmate and frequent co-author. Leigh introduced Baigent to the alleged Rennes-le-Chateau mystery in France, and Baigent launched into research on the matter. In the same decade, he met Henry Lincoln, a British television scriptwriter, while Lincoln was lecturing at a summer school. The three discovered that they shared a common interest in the Knights Templar, and took their Jesus bloodline theory on the road during the 1970s, in a series of lectures which later developed into the 1982 book, The Holy Blood and the Holy Grail.

Published on 18th January 1982, The Holy Blood and the Holy Grail popularised the hypothesis that the true nature of the quest for the Holy Grail was that Jesus and Mary Magdalene had a child together, the first of a bloodline which later married into a Frankish royal dynasty, the Merovingians, and was all tied together by a society known as the Priory of Sion. These theories were later used as a basis for Dan Brown's international bestselling novel The Da Vinci Code.

The day after the publication the authors had a public clash on television with the Bishop of Birmingham. The book rapidly climbed the bestseller charts, and a sequel, The Messianic Legacy, was published in 1986. The Holy Blood and the Holy Grail has reportedly, as of 2006, sold two million copies, with the film rights having been bought by Paramount.

Later, only with Baigent as co-author, he penned several books, as The Dead Sea Scrolls Deception (1991) in which they primarily follow the controversial theories of Dr. Robert Eisenman about the Dead Sea Scrolls.

Two books of Leigh's fictional works have been published: Erceldoune & Other Stories (2006), and Grey Magic (2007).

Leigh's sister is the author and successful astrologer Liz Greene.

Some of the ideas presented in Baigent's earlier book The Holy Blood and the Holy Grail, were incorporated in the bestselling American novel The Da Vinci Code, by Dan Brown.

In March 2006, Baigent and Leigh filed a lawsuit in a British court against Brown's publisher, Random House, claiming copyright infringement. On 7th April 2006 High Court judge Peter Smith rejected the copyright infringement claim by Michael Baigent and Richard Leigh, and Dan Brown won the court case. On 28th March 2007, Baigent and Leigh lost their appeal against this decision and were faced with legal bills of about 3 million pounds (see Guardian article).

Leigh died on 21st November 2007 in London from causes related to a heart condition.

Co-written with Michael Baigent and Henry Lincoln

• The Holy Blood and the Holy Grail, 1982, UK ISBN 0-09-968241-9
• U.S. paperback: Holy Blood, Holy Grail, 1983, Dell. ISBN 0-440-13648-2
• The Messianic Legacy, 1986

Co-written with Michael Baigent

• The Dead Sea Scrolls Deception, 1991
• The Temple and the Lodge, 1991, ISBN 0-552-13596-8
• Secret Germany: Claus Von Stauffenberg and the Mystical Crusade Against Hitler, 1994
• The Elixir and the Stone: The Tradition of Magic and Alchemy, 1997
• The Inquisition. 1999

• Erceldoune & Other Stories (2006, ISBN 978-1-4116-9943-4)
• Grey Magic (2007, ISBN 978-0-6151-3733-9).