Mary Hogarth Dickens' first child was named Mary in her memory. Hogarth was the daughter of George Hogarth (1783–1870), a music critic, cellist and composer, and Georgina Hogarth Thompson (1793–1863). She was born in Edinburgh, where her father was a legal advisor to Walter Scott, whom the young Charles Dickens greatly admired. She was the fourth of ten children, and the third daughter. Hogarth was named after her paternal grandmother. The name Mary Scott had previously been given to George and Georgina's third child, born 1817 or 1818, who was an infant when she died. Mary and her sister Catherine first met
David George Hogarth in 1927. In 1915, during the First World War, Hogarth was commissioned with the temporary rank of lieutenant commander in the Royal Naval Volunteer Reserve and joined the Geographical Section of the Naval Intelligence Division. Professor Hogarth was appointed the acting director of the Arab Bureau, for a time during 1916 when Sir Mark Sykes went back to London. Kinahan Cornwallis was his deputy. Hogarth was close with T. E. Lawrence and worked with Lawrence to plan the . Sykes befriended Hogarth, who had described India Government as believing they had a moral imperative to the British Raj as the