During the First World War, Montefiore volunteered in France but also joined the British Socialist Party, and contributed articles to "The Call". In 1920, she was elected to the provisional council of its successor, the Communist Party of Great Britain. When Montefiore's son died in 1921 from the effects of mustard gas poisoning acquired during his service in the War, the Australian government would not allow her to visit Australia until Holman spoke on her behalf and assured them that she promised not to engage in communist propaganda. Montefiore was allowed to visit, and also used the time to make connections in the Australian communist movement, meeting Christian Jollie Smith. Montefiore represented the Communist Party of Australia in Moscow in 1924.