Helena Sickert was the only daughter of the painter Oswald Sickert (technically of Danish nationality, though he always considered himself German and did not speak Danish) and the Englishwoman Eleanor Louisa Henry, an illegitimate daughter of astronomer Richard Sheepshanks, a Fellow of Trinity College, Cambridge and an Irish dancer. Helena's brother was the well-known painter Walter Sickert. As a schoolgirl, reading John Stuart Mill's On the Subjection of Women influenced her to become a feminist. She was educated at Girton College, Cambridge, and she married the Manchester University lecturer Frederick Swanwick in 1888.
Helena Swanwick worked as a journalist, initially as a sort of protegée of C.P. Scott, and wrote articles for the Manchester Guardian. In 1906 she joined the National Union of Women's Suffrage Societies in preference to the Women's Social and Political Union, because of her belief in non-violence. She quickly became prominent in the National Union, and was editor of its weekly journal, The Common Cause from 1909–1912. She remained on the NUWSS Executive until 1915. She was also a member of the Labour Party.
On the outbreak of World War I, she began campaigning for a negotiated peace. In 1915, together with such other prominent suffragists as Catherine Marshall and Agnes Maude Royden, she resigned from the National Union over its refusal to send delegates to the International Women's Congress at the Hague. She was one of the founding members of the Women's International League for Peace and Freedom. From 1914 she had already been active in the Union of Democratic Control. G. K. Chesterton would criticise her pacifism in the 2 September 1916 issue of Illustrated London News:
Mrs. Swanwick, the Suffragist who has reappeared as a Pacifist, has recently declared that there must be no punishment for the responsible Prussian. She puts it specifically on the ground that they were promised, or promised themselves, the conquest of the whole world; and they have not got it. This, she says, will be punishment enough. If I were to propose, to the group which is supposed to inspire the Pacifist propaganda, that a man who burgled their strong boxes or pilfered their petty cash should suffer no punishment beyond failing to get the money, they would very logically ask me if I was an Anarchist. If I proposed that anybody trying to knife or pistol another person should walk away and resume his daily amusements if the knife broke or the pistol missed fire, they would certainly ask me if I had contemplated the possibility of encouraging the employment of knives and pistols. Crime can be only insufficiently restrained when the alternative is between success and punishment. It could hardly be restrained at all if the alternative were only between success and failure; that is, between success and freedom—including freedom to try again.
This was not the only opposition she suffered both as a suffragist and internationalist, as she was subject to physical violence.
After the war she maintained her internationalist views, opposing the punitive terms of the Treaty of Versailles and serving as the United Kingdom substitute delegate to the League of Nations. In the 1930s she became increasingly depressed by the growing rationalist attitude of preparedness towards Fascist violence, which was increased by the death of her husband in 1934. After the outbreak of the Second World War she committed suicide with an overdose of veronal in November 1939.
Her autobiography I Have Been Young gives a remarkable account both of the non-militant women's suffrage campaign and of anti-war campaigning in the First World War, together with philosophical discussions of non-violence.
- The Future of the Women's Movement (1913)
- Builders of Peace, Being Ten Years History of the Union of Democratic Control (1924)
- Labour's foreign policy : what has been and what might be (1929)
- I Have Been Young, autobiography, (1935).
- The Roots of Peace: A Sequel to Collective Insecurity, Being an Essay on Some of the Uses, Condition (1938)