With Thérèse Casgrain, Roback fought for woman's suffrage in Quebec in 1936. In the same year, the International Ladies' Garment Workers' Union dispatched Rose Pesotta, a veteran union organizer from New York, to establish the ILGWU in Montreal. She was aided by Roback. The latter was uniquely helpful in uniting the garment workers owing to her ability to speak Yiddish, French, and English, and ultimately helped organize 5,000 garment workers who had been on a three-week strike in 1937. Roback helped unionize RCA Victor in 1941, where she remained until 1951. She won the first union contract for women in 1943 but did not want to become a union representative or climb up the union power structure.
