Teresa was born Anjezë Gonxhe (or Gonxha) Bojaxhiu; on 26 August 1910 into a Kosovar Albanian family in Skopje (now the capital of North Macedonia), Ottoman Empire. She was baptized in Skopje, the day after her birth. She later considered 27 August, the day she was baptised, her "true birthday".
Teresa was in her early years when she was fascinated by stories of the lives of missionaries and their service in Bengal; by age 12, she was convinced that she should commit herself to religious life. Her resolve strengthened on 15 August 1928 as she prayed at the shrine of the Black Madonna of Vitina-Letnice, where she often went on pilgrimages.
She arrived in India in 1929 and began her novitiate in Darjeeling, in the lower Himalayas, where she learned Bengali and taught at St. Teresa's School near her convent. Teresa took her first religious vows on 24 May 1931. She chose to be named after Thérèse de Lisieux, the patron saint of missionaries; because a nun in the convent had already chosen that name, Agnes opted for its Spanish spelling (Teresa).
On 10 September 1946, Teresa experienced what she later described as "the call within the call" when she travelled by train to the Loreto convent in Darjeeling from Calcutta for her annual retreat.
She began missionary work with the poor in 1948, replacing her traditional Loreto habit with a simple, white cotton sari with a blue border. Teresa adopted Indian citizenship, spent several months in Patna to receive basic medical training at Holy Family Hospital and ventured into the slums.
On 7 October 1950, Teresa received Vatican permission for the diocesan congregation, which would become the Missionaries of Charity. In her words, it would care for "the hungry, the naked, the homeless, the crippled, the blind, the lepers, all those people who feel unwanted, unloved, uncared for throughout society, people that have become a burden to the society and are shunned by everyone".
In 1952, Teresa opened her first hospice with help from Kolkata officials. She converted an abandoned Hindu temple into the Kalighat Home for the Dying, free for the poor, and renamed it Kalighat, the Home of the Pure Heart (Nirmal Hriday).
At the height of the Siege of Beirut in 1982, Teresa rescued 37 children trapped in a front-line hospital by brokering a temporary cease-fire between the Israeli army and Palestinian guerrillas. Accompanied by Red Cross workers, she travelled through the war zone to the hospital to evacuate the young patients.
On 13 March 1997 Teresa resigned as head of the Missionaries of Charity.
She died on 5 September.