On 12 March 1844, when aged only eighteen, Mundella married Mary, the daughter of William Smith, a warehouseman of Kibworth Beauchamp in Leicestershire. She was described as "a woman of lofty mind and great determination" and fully shared her husband's literary and artistic sympathies. Her "quiet, clever criticisms" were said to delight her guests and she was credited with an "unselfish, gentle, and sunny disposition" She died after a short illness on 14 December 1890. Their marriage was described as "outstandingly happy" and "blissful" and Mundella was said to have been "inconsolable" at his wife's death. "She was loved and honoured in an extraordinary degree by all from the highest to the humblest," Mundella wrote to his sister Theresa. "What a romance it all seems, Alas! What a terrible drama for me!" His manner after his bereavement was said to have become sharper and more intolerant, as observed by another MP in the House of Commons. Mundella and his wife had two children, Eliza Ellen, known in the family as "Nelly", who married Roby Thorpe of Nottingham, and Maria Theresa, known as "Pen", who remained single and lived at Elvaston Place until her death.