James David Graham Niven was born in London to William Edward Graham Niven (1878–1915) and Henrietta Julia Degacher. He was named David for his birth on St. David's Day (1 March). Niven often claimed that he was born in Kirriemuir, in the Scottish county of Angus in 1909, but his birth certificate shows this was not the case.
Henrietta was of French and British ancestry. She was born in Wales, the daughter of army officer William Degacher (1841–1879) by his marriage to Julia Caroline Smith, the daughter of Lieutenant General James Webber Smith. Niven's grandfather William Degacher was killed in the Battle of Isandlwana (1879), during the Zulu War. Born William Hitchcock, he and his brother Henry had followed the lead of their father, Walter Henry Hitchcock, in assuming their mother's maiden name of Degacher in 1874.
William Niven, David's father, was of Scottish descent; his paternal grandfather, David Graham Niven, (1811–1884) was from St. Martin's, a village in Perthshire. William served in the Berkshire Yeomanry in the First World War and was killed during the Gallipoli Campaign on 21 August 1915. He was buried in Green Hill Cemetery, Turkey in the Special Memorial Section in Plot F. 10.
David's mother Henrietta then married Sir Thomas Comyn-Platt in London in 1917. Graham Lord, in Niv: The Authorised Biography of David Niven, suggested that Comyn-Platt and Mrs. Niven had been having an affair for some time before her husband's death, and that Sir Thomas may well have been David Niven's biological father, a supposition which has some support from her children. A reviewer of Lord's book stated that Lord's photographic evidence showing a strong physical resemblance between Niven and Comyn-Platt "would appear to confirm these theories, though photographs can often be misleading.”
David Niven had three older siblings:
- Margaret Joyce (born in Geneva, Switzerland, 5 January 1900 – 18 November 1981)
- Henry Degacher ("Max"; born in Buckland, Berkshire 29 June 1902 – March 1953)
- Grizel Rosemary Graham (born in Belgravia, Middlesex), 28 November 1906 – 28 January 2007).
The source for the dates and places of birth of the above is William Edward Graham Niven's army service record which does not give a place of birth for David, but his birth certificate states Belgrave Mansions, London. The family's country home at Buckland, Carswell Manor, was sold shortly after David's birth.