Thomas Arthur Ponsonby, 3rd Baron Ponsonby of Shulbrede (23 October 1930 – 13 June 1990) was a British hereditary peer and Labour Party politician.

He was the eldest son of Matthew Henry Herbert Ponsonby, 2nd Baron Ponsonby of Shulbrede, and his wife Hon. Elizabeth Mary Bigham, daughter of the 2nd Viscount Mersey. He was educated at Bryanston School and Hertford College, Oxford.

He served in London local government for 20 years, firstly as a council member of the Metropolitan Borough of Kensington from 1956 to 1965 and then as an Alderman of the newly created Kensington and Chelsea London Borough Council from 1964 to 1974. He was also an Alderman of the Greater London Council from 1970 to 1977 and served as the Chairman of the Council from 1976 to 1977.

Ponsonby succeeded to the peerage on the death of his father in 1976 and made his maiden speech in the House of Lords on the subject of local government devolution.^[1] He was elected as Labour Chief Whip in the House of Lords in 1982, defeating Lord Strabolgi. He served as Opposition Chief Whip until his death in 1990.

Ponsonby was an active member of the Fabian Society, serving as its general secretary from 1964 to 1976, and was a Governor of the London School of Economics from 1970 to 1990.^[2]

He had married twice:

• firstly Ursula Mary Fox-Pitt, the daughter of Cdr Thomas Stanley Lane Fox-Pitt of Devon, with whom he had a son and three daughters, and
• secondly Maureen Estelle Campbell-Teich, the widow of Dr Paul Campbell-Teich of Geneva, Switzerland.

He was succeeded by his son, Frederick Ponsonby, 4th Baron Ponsonby of Shulbrede.^[3]