Lily H. Montagu's spiritual journey from Orthodox Judaism to founding the Liberal Jewish movement in England illuminates a pivotal transformation in Anglo-Jewish religious life during the early twentieth century. A teenage spiritual crisis, combined with the theological influence of Claude Montefiore and her dedication to social service, led Montagu (1873-1963) to reject Orthodox practice in favor of a more personal, spiritually-oriented faith. Drawing on her writings, correspondence, and organizational records from the Jewish Religious Union and Liberal Jewish Synagogue archives, this research reveals how Montagu navigated the delicate balance between tradition and reform. In 1902, she established the Jewish Religious Union, initially offering supplementary Liberal services while attempting to maintain community cohesion. Growing Orthodox opposition by 1909 compelled the organization to embrace an explicitly Liberal Jewish identity, culminating in the Liberal Jewish Synagogue's founding in 1912. Montagu's influence ultimately transcended national boundaries through her leadership of the World Union for Progressive Judaism, where she served as President from 1954-1959. Her remarkable combination of practical organizational skills and mystical spiritual leadership enabled her to shape both individual religious experiences and establish enduring institutional frameworks for Liberal Judaism worldwide.