At age 11, Tosia Altman joined the local chapter of Hashomer Hatzair, which soon became the center of her life, and at the age of 14 she was selected to serve as a counselor in the movement. Later, she underwent agricultural training in Częstochowa and impatiently awaited the day she would fulfill her goal of emigrating to Palestine. But her move to Palestine was delayed by the exigencies of the movement, which needed her to continue her work in Poland. On the eve of the war, Tosia was selected to head up a secondary movement leadership that was meant to begin operating in the event of a state of emergency.
Immediately after the fall of Poland in September 1939, Tosia joined the concentration of Hashomer Hatzair members in Vilna. When the troubling reports regarding the fate of the Jews of Poland, the paralysis of movement chapters in the country, and their young members left without leadership and guidance in face of the new realities of German occupation, she was one of the first to return to occupied Warsaw. Tosia was a talented and sensitive young woman, and, in addition to her efforts to reorganize movement work for underground conditions, she published articles in the underground movement press and became one of the movement's most important emissaries to ghettos throughout occupied Poland. Her travels, which were all undertaken using falsified documents, were filled with anxiety and fear. Only upon reaching Jewish surroundings and feeling the breath of fellow Jews around her did Tosia's familiar smile return to her face, once again radiating warmth and comfort.
After the establishment of the Jewish Fighting Organization, the ŻOB, Tosia was sent to the Aryan side of the city to carry out the dangerous and sensitive mission of acquiring weapons and smuggling them into the ghetto. With every rumor of an impending action, Tosia would return to the ghetto, as she did on the eve of the Passover holiday in 1943. At this point, Tosia was integrated into the ŻOB command and was responsible for communications with Antek Zuckerman, the ŻOB's representative outside the ghetto. After the Germans started burning down the houses in the ghetto, Tosia, accompanied by Mordechai Anielewicz, visited wounded comrades in the bunker at 30 Franciszkanska Street.
Tosia was injured during the Warsaw Ghetto Uprising in April 1943. She was among the few fighters who managed to escape the ghetto via the sewer system after the discovery of the bunker at 18 Mila Street in which the last remaining ŻOB fighters had taken refuge. On May 24, 1943, a fire broke out in the fighters' hiding place, and some were killed in the raging inferno. Others were captured by the policemen and firefighters who arrived on the scene. Tosia and a friend named Shifra were taken into custody and handed over to the Germans, who brought them to the hospital. After a few days of being tortured, both died of their injuries.
In An excerpt from Tosia's final coded letter to a friend in Palestine, April 7, 1942, she wrote : “The Jewish People are dying before my eyes, and I wring my hands, unable to help it."