Gregson, from Monmouthshire, has a background in journalism
Julia Gregson has been announced as the winner of this year's Romantic Novel of the Year for her book East of the Sun.
The novel tells the story of three women in the last days of the British Raj in India.
Judges said it engaged "from the first page and never let go, following their various fortunes until it reached its truly satisfying ending".
The prize was presented to Gregson at the Romantic Novelists' Association awards lunch in London.
The judges praised the depiction of "three remarkable women at its centre, each with different flaws, strengths and voices".
"The last days of the British Raj in India, at a pivotal moment of its history during the ascendancy of Gandhi, were brilliantly evoked in the author's skilled hands," they added.
Gregson, from Monmouthshire, has a background in journalism and spent time working as a correspondent in India.
The winner of the Romance Prize for shorter works of fiction was Mistress: Hired for the Billionaire's Pleasure by India Grey.
Judges said they were impressed by the "sheer verve and style" of the book which they described as "a model of romance, well-written and memorable with a clever plot featuring a lovely heroine and a gorgeous hero".
Independent publisher Judy Piatkus, meanwhile, was honoured with an inaugural lifetime achievement award.
The Romantic Novelists' Association said many of its members owed their writing careers to her publishing company, Piatkus Books.
"Judy was never afraid to take a chance on an unknown whose work she believed in," chairman Catherine Jones said.
Last year's winner of the main award was Pillow Talk by Freya North.
The Romantic Novel of the Year award was introduced in 1960 by the association to recognise excellence in romantic fiction and to enhance the standing of the genre.