Early life and education. He was the second son of William Ponsonby, who was created Baron Ponsonby of Imokilly in 1806, and Hon. Louisa Molesworth. He was the grandson of politician Hon. John Ponsonby and great-grandson of the 3rd Duke of Devonshire and the 1st Earl of Bessborough.
The Guest family is a British family that has been prominent in business and politics since the 18th century. It was involved in the British iron and steel industry, particularly the Dowlais Ironworks in Wales, which later became part of Guest, Keen and Nettlefolds.