Arthur Mountifort Longfield Ponsonby, 11th Earl of Bessborough (11 December 1912 – 5 April 2002), was a British peer.

He inherited the earldom on 5 December 1993 when his first cousin, Frederick Ponsonby, 10th Earl of Bessborough, died without a male heir.

Later he rose to the rank of captain in the service of the Welsh Guards and saw action in the Second World War.

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.

[5] He died on 5 April 2002 and was succeeded by his eldest son Myles Ponsonby, who became the 12th Earl of Bessborough.