She was born on 21 October 1867 in Bristol, her Cornish father becoming a lapsed Methodist. Educated at a boarding school, she became a Suffragette leader who developed her social activism, politics and public speaking when working for H.P. Hughes as a 'Sister of the People' at the Cleveland Hall in the WM West London Mission. Her first attempt at public speaking was at the 1891 anniversary. At Cleveland Hall she helped Mary Neal run a club for working girls. They were encouraged by Mark Guy Pearse in their independent venture, the Espérance Girls' Club, where girls could experience dance and drama without the constraints of the Mission.
In 1905/6 she met the Pankhursts and was drawn into the Suffragette movement, for which she suffered six periods of imprisonment, becoming the Treasurer of the Women's Social and Political Union, getting support in this from her husband, whom she had married in 1901. They were both ousted by the Pankhursts for opposing their more radical - at times, violent - forms of activism and then joined the United Suffragists. During and after World War I she became involved in the peace movement; from 1915 to 1922 she was treasurer of the Women's International League for Peace and Freedom and from 1926 to 1935 was President of the Women's Freedom League.
After her marriage in 1901 to a kindred spirit, Frederick Lawrence (1871-1961), they adopted the joint name of 'Pethick-Lawrence'. In later years her career tended to be eclipsed by his and by prolonged ill health. She died at Gomshall, Surrey on 11 March 1954. The son of a wealthy Unitarian, Eton and Cambridge educated, he was a barrister and initially a Liberal who became a socialist. From 1923 to 1931 he was Labour MP for Leicester West and from 1935 to 1945 for Edinburgh East. He was the Financial Secretary to the Treasury, 1929-1931. Elevated to the peerage in 1945, he was Secretary of State for India, 1945-1947.