Marianne Thornton (10 March 1797 – 5 November 1887) was an English Human rights activist, who campaigned for the abolition of slavery.
Marianne Thornton was the eldest of nine children of the English philanthropist, economists and abolitionists Henry Thornton (1760–1815) and his wife Marianne Sykes (1765–1815). Her father, MP for Southwark, was next to William Wilberforce to the Clapham Saints, an influential group of members of the Church of England. After the early death of both parents in 1815, she and her siblings grew up by a family friend, the politician Sir Robert Inglis. She spent most of her life in Clapham and was one of the Bluestockings.
Marianne Thornton was the head of the Thornton family. She was the paternal great-aunt of E. M. Forster, to whom she inherited the sum of £8,000 (the equivalent of about £990,000 in 2017) as a legacy in trust after her death. Forster published about her in 1956 a detailed biography. Thornton became nationally known through the publication of Forster.
- John Wolffe, ‘Inglis, Sir Robert Harry, second baronet (1786–1855)’, Oxford Dictionary of National Biography, Oxford University Press, 2004 accessed 26 September 2019
- UK Retail Price Index inflation figures are based on data from Clark, Gregory (2017). "The Annual RPI and Average Earnings for Britain, 1209 to Present (New Series)". MeasuringWorth. Retrieved 2 February 2020.
- "A Chronology of Forster's life and work". Cambridge.org. 1 December 1953. Retrieved 26 September 2019.
- E. M. Forster: Marianne Thornton, 1797–1887. A Domestic Biography. Arnold, London 1956