Anjeze Gonxhe Bojaxhiu was born on 26 August 1910 in Skopje, then part of the Ottoman Empire and now the capital of North Macedonia, to an Albanian Catholic family. She joined the Sisters of Loreto in Ireland in 1928, taking the name Teresa after Therese of Lisieux, and was sent that same year to India, where she taught for nearly two decades at a Loreto convent school in Calcutta.
In 1946, travelling by train to a retreat in Darjeeling, she experienced what she later described as a call within her calling, an instruction to leave the convent and work directly among Calcutta's poorest residents. She received permission to do so in 1948, left the Loreto order, trained briefly as a nurse and began work alone in the city's slums, wearing for the first time the simple white sari bordered in blue that became her lifelong habit and, eventually, an internationally recognized symbol. The years that followed were difficult ones: she begged for food and supplies from local merchants, slept wherever shelter could be found, and was joined only gradually by former students and other volunteers willing to share the same austere conditions. That slow, uncertain beginning, rather than any sudden institutional backing, is what the earliest Missionaries of Charity accounts describe, and it shaped the congregation's later insistence on living among, rather than merely visiting, the people it served.