[3] Brion was active in various feminist organizations for most of her life, fighting for equal legal rights for women and for the vote.

With the outbreak of World War I in July 1914 the teachers' union office was reduced to Brion as acting secretary general and Fernand Loriot as treasurer.

He devoted much effort to fighting the nationalist unions that supported the war, along with Alphonse Merrheim, Albert Bourderon and Raymond Péricat.

[1] On 15 August 1915 a pacifist resolution was presented at the CGT's national congress at the initiative of Albert Bourderon and Alphonse Merrheim, signed by several militants of the federation of teachers' unions including Louis Bouët, Fernand Loriot, Marie Guillot, Marie Mayoux, Marthe Bigot and Hélène Brion.

[1] In 1917, Louise Bodin and Colette Reynaud founded the journal La Voix des femmes, to which the major feminists contributed including Nelly Roussel and Hélène Brion.

[8] A police report in 1917 described "the activist Hélène Brion, public school teacher in Pantin, general secretary of the National Federation of public school teachers (Fédération Nationale des instituteurs et institutrices publics), a member of the Committee for the resumption of international relations (Comité pour la reprise des relations internationales) and a member of union defense committee (Comité de défense syndicaliste).

[1][a] The national syndicalist journalist Émile Janvion published an undated pamphlet, probably in late 1917, titled Le féminisme défaitiste (Defeatist Feminism).

He identified pro-peace feminist leaders such as Hélène Brion, Séverine, Marguerite Durand, Hubertine Auclert and Nelly Roussel, and wrote, "the history of defeatism, when it is known, will demonstrate superabundantly that feminism will there merit, I dare say, the place of honor.

"[12] Madeleine Vernet organized a defense committee for Hélène Brion, who was secretary of the board of her workers' orphanage L'Avenir social at Épône.

She wrote, "From this tissue of infamies it came out that Hélène Brion was a dangerous and suspicious character—Anarchist, revolutionary, Malthusian, anti-militarist, defeatist.

[14] A general assembly of militants was held on 17 December 1917, which issued a manifesto in Brion's favor and raised a subscription.

The charges were based on a law of 5 August 1914 that prohibited publications that would give information to the enemy or would exercise a bad influence on the mind of the army and the people.

Character witnesses included Séverine, Jean Longuet, deputy and grandson of Marx, Marthe Bigot, a teacher who said she had distributed the same material as Brion and therefore deserved the same punishment, Nelly Roussel, vice president of the Union fraternelle des femmes and others.

The defense stated that the offending leaflets were not illegal and had been openly circulated for a long time without the authorities taking any action.

But he reminded the court that Brion's actions were to be judged, not her moral character, and insisted that blind pacifism is defeatism.

Brion's lawyer asked that if the court found her guilty, it should be lenient: "if she made a mistake, she did it without personal interest, she was mistaken out of goodness, the nobility of her soul."

Hélène Brion does not seem to have attended the Second Congress of the Comintern in June–July 1920, but arrived before the end of the summer of 1920 and returned to France in late January or early February 1921.

[21] As a relatively minor figure, she was somewhat isolated from the main political players and events in Russia, but was able to obtain a brief interview with Lenin in the Kremlin.

The many boxes of material, including biographical notes, newspaper clippings, postcards, poorly organized and without citations, is held in the Bibliothèque Marguerite Durand.

A letter survives from November 1944 in which she asks a member of the newly elected Constituent Assembly to support women's rights.

She said she was proud of her fellow citizenesses, who could not be equalled in the war, and that the FLN would work to rebuild the country and establish world peace.