Born in Vienna, Stein was of Jewish heritage, the daughter of Sophie Bachmann and musician Erwin Stein. She came to the UK just before the Second World War. "She attended the Royal College of Music and became good friends with composer Benjamin Britten."  She was the joint founder in 1961 (along with Fanny Waterman) of the Leeds International Pianoforte Competition. In 1973, she was a guest on BBC Radio 4's Desert Island Discs and she was an occasional panellist on the BBC music quiz Face the Music.
Stein married twice, on both occasions to prominent public figures.
Her first husband was George Lascelles, 7th Earl of Harewood (married 29 September 1949). Lord Harewood, son of Mary, Princess Royal, was the grandson of King George V, the nephew of kings Edward VIII and George VI, and the cousin of Queen Elizabeth II. As a result of this marriage, Marion gained the title Countess of Harewood. They had three sons:
- David Lascelles, 8th Earl of Harewood (born 21 October 1950)
- James Lascelles (born 5 October 1953)
- Jeremy Lascelles (born 14 February 1955)
By 1959, there were serious problems in the marriage. Harewood began a relationship with violinist Patricia Tuckwell, but Stein rejected the idea of divorce until 1967, by which time he had a son by Tuckwell. His adultery and remarriage made him a social outcast for several years, and it was ten years before he was invited to any events by the Royal Family.
Stein's second husband was Jeremy Thorpe (married 1973). Thorpe was then a Member of Parliament and Leader of the Liberal Party. His first wife, Caroline, had been killed in a car accident in 1970. Stein stood by Thorpe throughout the "Rinkagate" scandal of the late 1970s. Shortly afterwards, Thorpe was diagnosed as suffering from Parkinson's disease, and Marion also had mobility problems.
Marion Thorpe died on 6 March 2014 at the age of 87.
- John Amis (2014-03-07). "Marion Thorpe obituary | Politics". The Guardian. Retrieved 2014-03-07.
- Reed, Philip; Cooke, Mervyn (2010). Letters from a Life: the Selected Letters of Benjamin Britten, 1913–1976; Vol 5. Boydell Press. p. xlv. ISBN 1-84383-591-6.
- Obituary: The Earl of Harewood. The Telegraph, 11 July 2011. Accessed 16 February 2013
- Peter, NDJ (9 March 2014), "Marion Thorpe, wife of former North Devon MP and Liberal leader Jeremy Thorpe, dies at age 87", North Devon Journal (Barnstaple), archived from the original on 2014-03-09 
- Cummings, David (2000). International Who's Who in Music: and Musicians' Directory Vol. 1. Routledge. p. 640. ISBN 0-948875-53-4.
- BBC - Desert Island Discs, BBC Radio 4, 29 December 1973.
- Royal Musings: "Adultery, a child, divorce, remarriage = estrangement from the Royal Family ", 12 July 2011. Accessed 16 February 2013
- "The downfall of Jeremy Thorpe", Express, 8 May 2009. Accessed 16 February 2013.
- "Jeremy Thorpe - Former Liberal Party Leader in the UK", BBC News.
- "Marion (née Stein), Countess of Harewood, later Mrs Jeremy Thorpe". National Portrait Gallery. Retrieved 21 June 2011.