Mary Steel Stevenson MBE, née Kelly (21 August 1896 – 3 July 1985) was a Scottish-born Australian community and political activist.
She was born in Maybole in Scotland, attending North Kelvinside School in Glasgow. In January 1925 she married Robert Stevenson, and they emigrated to Queanbeyan in New South Wales in March 1925, moving to the Canberra suburb of Griffith in 1926. The couple had one son, John. Stevenson was involved with the Citizens' Rights League, a group formed in 1927 to advocate for federal parliamentary representation for the Australian Capital Territory; she lobbied Prime Minister John Curtin for the League.
She was a commandant of No. 750 Voluntary Aid Detachment during the Second World War, and was awarded a citation from the Duchess of Gloucester in her capacity as spouse of the Governor-General. She was also awarded a Red Cross Medal for her work as an executive member of the ACT's Red Cross Society. From 1940 to 1942 she was President of the Young Women's Christian Association of Canberra. After the war she was elected to the board of Canberra Community Hospital, and also served on the ACT Tourist Bureau Advisory Board and as Girl Guides Divisional Commissioner.