Mary Hobhouse was married to Lord Arthur Hobhouse, who served on the Viceroy's Legal Council in India. Upon their return to England in 1877, they became members of the National Indian Association. Mary Hobhouse often chaired the committee meetings of the Association, particularly from 1886 until 1901. She and her husband were leading figures of the Association until they died within months of each other in 1904 and 1905. The couple had no children.

After Cornelia Sorabji wrote to the National Indian Association in 1888, Lady Hobhouse was instrumental in raising funds for Cornelia Sorabji to study in Britain. Hobhouse wrote a letter to The Times and established a fund that was also advertised in the Queen. Contributors included E. A. Manning, Florence Nightingale, Madeleine Shaw Lefevre, Sir William Wedderburn and many other British figures. When Sorabji came to England in 1889, the Hobhouses saw Sorabji regularly and encouraged her to take up the teaching and then the legal line rather than medicine as Sorabji had originally envisaged.

Mary Hobhouse often contributed to the Journal of the National Indian Association (Indian Magazine at this time). Contributions included a review of Manmohan Ghose and Laurence Binyon's Primavera in 1890 and an edited selection of extracts from the diary of Mehdi Hasan Khan's visit to London in the same year.