Mary met John Maxwell (1824–1895), a publisher of periodicals, in April 1861 and moved in with him in 1861.Victor E. Neuburg, The Popular Press Companion to Popular Literature, Popular Press, 1983. , pp. 36–37. However, Maxwell was already married to Mary Ann Crowley, with whom he had five children. While Maxwell and Braddon were living as husband and wife, Crowley was living with her family. In 1864, Maxwell tried to legitimize their relationship by telling the newspapers that they were legally married; "however, Richard Brinsley Knowles wrote to these papers, informing them that his sister-in-law and true wife of Maxwell was still living, thereby exposing Braddon's 'wife' status as a façade". Mary acted as stepmother to his children until 1874, when Maxwell's wife died and they were able to get married at St. Bride's Church in Fleet Street. Braddon had six children by him: Gerald, Fanny, Francis, William, Winifred Rosalie, and Edward Herry Harrington.
