She was born Margaret Thyra Barbara Shore Smith (later Shore Nightingale). Margaret studied History at Girton College, Cambridge, 1891–1894. In 1904 she married Harry Lushington Stephen, later Sir Harry Stephen (1860–1945). In India with her husband 1904–1913, she founded the Women Graduates Union in Calcutta for the benefit of professional women coming to India. She was a member of Girton College Council 1913–1932, Governor of Girton College 1913–1938, and a generous benefactor of Girton Library.