| Honorific Prefix: | The Right Honourable |
| The Earl of Bessborough | |
| Office: | Member of the House of Lords |
| Status: | Lord Temporal |
| Term Start: | 1994 |
| Predecessor: | The 10th Earl of Bessborough |
| Term End: | 11 November 1999 |
| Successor: | Seat abolished |
| Birth Name: | Arthur Mountifort Longfield Ponsonby |
| Birth Date: | 11 December 1912 |
Arthur Mountifort Longfield Ponsonby, 11th Earl of Bessborough (11 December 1912 – 5 April 2002), was a British peer.
He was the son of Maj. Hon. Cyril Myles Brabazon Ponsonby, second son of Edward Ponsonby, 8th Earl of Bessborough, and his wife Rita Narcissa Longfield, daughter of Lt. Col. Mountifort John Courtenay Longfield. He inherited the earldom on 5 December 1993 when his first cousin, Frederick Ponsonby, 10th Earl of Bessborough, died without a male heir.
He was educated at Harrow School and Trinity College, Cambridge. Later he rose to the rank of captain in the service of the Welsh Guards and saw action in the Second World War. In his later years he farmed at Roche Court, Winterslow, Wiltshire.[1]
On 28 July 1939, he married Patricia Minnigerode (died 12 September 1952),[2] daughter of Col. Fitzhugh Lee Minnigerode of New York and Alexandria, Virginia. Together they had two children:
Following the death of his first wife, he remarried, on 20 September 1956, Anne Marie Galitzine (1916–2007; née von Slatin), former wife of Prince George Galitzine and daughter of Lt. Gen. Sir Rudolf Carl von Slatin (Baron von Slatin). They were divorced in 1963.
He married for the third time on 17 December 1963, Madeleine Lola Margaret Grand, daughter of Maj. Gen. Laurence Douglas Grand, and together they had two children:
Lady Bessborough is the founder of the New Art Centre, formerly of Sloane Street, London, which runs the New Art Centre Sculpture Park and Gallery at Roche Court, Wiltshire.[3] She is a trustee of the Roche Court Educational Trust charity. She was awarded a CBE in the 2023 New Year's Honours list.[4]
He died on 5 April 2002 and was succeeded by his eldest son Myles Ponsonby, who became the 12th Earl of Bessborough.