Born in Russia, Morris Sigman spent his youth working as a lumberjack before moving to London in 1902. In 1903, Sigman emigrated to New York City and began work as a presser in the cloak industry. He organized the Independent Cloak and Skirt Pressers' Union (1904) and allied it with the Socialist Trade and Labor Alliance. In 1905, the Independent Cloak and Skirt Pressers' Union was one of the founding unions of the Industrial Workers of the World (IWW), but by 1908, the union had left the IWW and joined the ILGWU.
Shortly after joining the ILGWU, Morris Sigman began to hold local and then national held leadership roles within the union. Sigman had been heavily involved in the garment workers' strikes of 1910, and was later arrested for murder in what became known as the "Trial of Seven Cloakmakers." With Morris Hillquit as their defense attorney, he and other other cloakmakers were found not guilty in 1915. Sigman served as the manager of Local 35 New York Cloak Pressers Union (1913), and then general manager of the Joint Board of Cloakmakers in New York City (1917-1921). At the international level, Sigman was a vice president of the ILGWU (1910-1913), before becoming Secretary-Treasurer (1914-1915) and first vice president (1920-1923). He was elected president of the ILGWU in 1923.
Sigman's tenure as president of the ILGWU was a tempestuous one in which the union faced a long and bitter internal struggle with Communist members for control of the organization. A lengthy strike of New York Cloakmakers in 1926 proved to be another costly battle for the union during this period. But Sigman's term was also marked by some significant accomplishments, including a reform effort that made possible substantial union contributions to the restructuring of the garment industry.