Ruth was born in Highgate, London, into a Quaker family - her father was Sir Edward Fry, a judge and lawyer who became known worldwide for his skilled work as a negotiator at the Hague Tribunal in 1907 - and she was educated at home. She then worked as a peace activist and a writer, serving as treasurer of the Boer Home Industries Commission during the Boer War, as general secretary of the Friends War Victims Relief Committee (a committee organized by British Quakers to provide help for refugees and victims of the First World War) from 1914 to 1924, as first chairman of the Russian Famine Relief Fund in 1921, as the secretary for the National Council for the Prevention of War in 1926-27, and as the treasurer of the London branch of the War Resisters' International in 1936-1937.
In the First World War she toured the war zones as a traveling commissioner, writing about the relief efforts in her book A Quaker Adventure (1926). She was appointed to the editorial board of the Fellowship of Reconciliation's journal Reconciliation in 1935.
- The Times, Saturday, Apr 28, 1962; pg. 12; Issue 55377; col B: OBITUARY-Miss Ruth Fry Relief Work With The Quakers.