On 18 May 1863, Heinemann was born in Surbiton, Surrey, England. Heinemann's father Louis Heinemann, a director of Parr's Bank and a native of Hanover, Germany. Heinemann's mother was Jane Lavino. Both his parents were Jewish by descent, although they had been Anglican for two generations. In his early life he wanted to be a musician, either as a performer or a composer, but, realising that he lacked the ability to be successful in that field.
Heinemann took a job with the music publishing company of Nicolas Trübner. When Trübner died in 1884, Heinemann founded his own publishing house in Covent Garden in 1890. The company published many translations of the classics in Great Britain as well as publishing such authors as H. G. Wells, Robert Louis Stevenson, Rudyard Kipling and Sylvia Plath.
On 2 February 1899, Heinemann married Magda Stuart Sindici, a writer who used the pseudonym Kassandra Vivaria, at St. Antonio's Church in Anzio, Italy. Her father was Augusto Sindici, an Italian poet. Her mother was Francesca Stuart Sindici, a Spanish-Italian painter. Wedding guest included James Abbott McNeill Whistler, a painter. Whistler attended their wedding as the bestman and painted the bride's portrait in 1900. In 1904, Heinemann divorced his wife. On 5 October 1920, Heinemann died unexpectedly in London, England.  Heinemann had no children and his presumptive heir, his nephew John Heinemann, had died in the First World War. Heinemann's share of the company was bought out by Frank Nelson Doubleday, the New York publisher.
- "William Heinemann, English Publisher". britannica.com. Retrieved June 23, 2019.
- Fritschner, Linda Marie (2004). "Heinemann, William (1863–1920)". Oxford Dictionary of National Biography. Oxford University Press. Retrieved 12 March 2013.
- Sindici, Augusto (February 22, 1899). "Wedding Invitation to Mr. Whistler". whistler.arts.gla.ac.uk. Retrieved June 23, 2019.
- "Magda Stuart Heinemann, m 1899". whistler.arts.gla.ac.uk. Retrieved June 23, 2019.
- Hall Caine: Portrait of a Victorian Romancer by Vivian Allen, Sheffield: Sheffield Academic Press, 1997, pp.373-384