In 1917, After spending several years in the United States, where according to Emma Goldman, "she gave all her spare time and a goodly part of her meagre earnings in a factory to further Anarchist propaganda," Baron returned to post-revolution Russia. She, along with her husband Aaron Baron, was deeply active in the Ukrainian Anarchist Confederation.
She could perform the most difficult task and deprive herself of the last piece of bread with grace and utter selflessness. Under harrowing conditions of travel, Fanya went up and down the Ukraine to spread the Nabat, organize the workers and peasants, or bring help and succour to her imprisoned comrades. —Emma Goldman
In 1920, when the Soviets began a harsh crackdown on Anarchists, Baron, her husband and several others were arrested and sent to Ryazan prison. She was severely beaten during the arrest. Held without charges under terrible conditions—lice, filth and disease were everywhere—they went on a hunger strike in 1921 which attracted worldwide attention.
At some point in late 1921, Baron escaped the prison and sought shelter in Moscow with her husband's brother, a Bolshevik, who promptly betrayed her. She was soon re-captured by the Cheka. On September 29, 1921, Baron and nine other prisoners including poet Lev Tcherny were executed. It was said that Baron's execution was on the personal order of Lenin.
Emma Goldman described her as "the type of . . . woman completely consecrated to the cause of humanity."