Mother Teresa, known as the "saint of the gutters," has been declared a saint of the Roman Catholic Church by Pope Francis at a canonisation ceremony held in Vatican City on Sunday.
Tens of thousands of pilgrims gathered in St. Peter’s Square for a service to honour the Albanian-born nun who died in 1997.
After a brief description of her work was read by Cardinal Angelo Amato, the Pope canonised Mother Teresa in the name of the Church.
"After due deliberation and frequent prayer for divine assistance, and having sought the counsel of many of our brother bishops, we declare and define Blessed Teresa of Calcutta to be a saint and we enrol her among the saints, decreeing that she is to be venerated as such by the whole Church," Francis said during the ceremony.
Francis described Teresa as a "dispenser of divine mercy," in a homily he delivered after completing the canonisation process.
He said Mother Teresa put into action his ideal of the church as a merciful "field hospital" for the poorest of the poor, those suffering both material and spiritual poverty.
"For Mother Teresa, mercy was the salt which gave flavour to her work, it was the light which shone in the darkness of the many who no longer had tears to shed for their poverty and suffering," he said.
Mother Teresa was born in 1910 in the Macedonian capital, Skopje which was then part of the Ottoman Empire.
In 1928, she joined the Sisters of Loreto in Ireland and then went to Indian city Kolkata to help the destitute.
In 1950, she established the Missionaries of Charity, a Roman Catholic Latin Rite religious congregation which is now active in more than 200 countries.
She won Nobel Peace Prize in 1979 for her efforts in alleviating poverty. She rejected the conventional ceremonial banquet given to laureates, asking that the funds to be given to poor people in India.
She was beatified in 2003 by Pope John Paul II, the first step towards her being declared a saint today.
The Church confers sainthood on people who were considered so holy during their lives that they are now believed to be in Heaven and can intercede with God to perform miracles.
Mother Teresa is credited with healing an Indian woman from stomach cancer in 1998 and a Brazilian man from a brain infection in 2008.
With two Church confirmed miracles in tow, the requirements for sainthood were met, but not everyone is convinced.
Critics claim that she was not eligible for sainthood as the healings resulted from medical treatment.
Some criticise her for accepting money from dictators and allegedly doing little to tackle the main causes of poverty.
She was also accused of trying to convert poor Hindus in India to Christianity, but her mission repeatedly denied this.