Winston Mawdsley Graham OBE, born Winston Grime (30 June 1908 – 10 July 2003), was an English novelist best known for the Poldark series of historical novels set in Cornwall, though he also wrote numerous other works, including contemporary thrillers, period novels, short stories, non-fiction and plays. Graham was the author's pseudonym until he changed his name by deed poll from Grime to Graham on 7 May 1947.

Graham was born in Victoria Park, Manchester, on 30 June 1908 to Ann Mawdsley, and Albert Grime, a prosperous tea importer and grocer. In 1921, Graham's father became incapacitated by a stroke in the same month that Graham contracted lobar pneumonia and on medical advice was educated at a local day school, Longsight Grammar School, which was near to home, rather than Manchester Grammar School which his father had in mind for him.

In 1925, when he was 17 years old, the family moved to Perranporth, Cornwall, where Graham lived for 34 years. He had wanted to be a writer from an early age and, following the death of his father in 1927, he was supported by his mother while he wrote novels at home in longhand and attempted to get them published. Graham's first novel, The House with the Stained Glass Windows, was published in 1934. In September 1939, Graham married Jean Williamson, having first met her in 1926 when she was 13 years old. His wife often helped Graham with ideas for his books, and the character of Demelza, in his Poldark series, was based in part on her. Graham's daughter said, "Father was the author but my mother helped with the details because she was very observant. She saw everything and remembered it all."

In 1940, near the start of the Second World War, Graham applied to join first the Navy, then the Army, but both times failed the medical. In 1941 he joined the Auxiliary Coastguard Service. He lived in Perranporth until January 1960, then briefly, during the summer of 1960, in the south of France before finally settling in East Sussex. He was a member of the Society of Authors from 1945, chairman of the Society's Management Committee from 1967 to 1969 and a fellow of the Royal Society of Literature. In 1983, he was made an Officer of the Order of the British Empire.

His wife died in 1992. They had two children, economist Andrew Graham and Rosamund Barteau. Graham died on 10 July 2003, aged 95, at his house, 'Abbotswood' in Buxted, East Sussex. His autobiography, Memoirs of a Private Man, was published in September of that year.

The Royal Cornwall Museum in Truro, Cornwall had an exhibition devoted to his life and works (Poldark's Cornwall: The Life and Times of Winston Graham) from mid-June to mid-September 2008 to celebrate the centenary of his birth, coinciding with re-publication of the Poldark novels by Pan Macmillan. Additionally, the Winston Graham Historical Prize was initiated as part of the Centenary Celebrations, funded by a legacy from the author and supported by Pan Macmillan. It is awarded for a work of unpublished fiction, preferably with an association with Cornwall. Details can be obtained from the Royal Cornwall Museum.

The majority of Winston Graham's manuscripts and papers have been donated to the Royal Institution of Cornwall by his son Andrew Graham and daughter Rosamund Barteau. Further papers are housed at the Howard Gotlieb Archival Research Center at Boston University and elsewhere.

His first Poldark novel, Ross Poldark, was published in 1945 and was succeeded by 11 further titles, the last of which, Bella Poldark, was published in 2002. The series was set in Cornwall, especially in and near Perranporth where Graham lived for more than three decades (1925–1960).