"She bowed down before those who were spent, left to die on the side of the road, seeing in them their God-given dignity", the pope said. Francis followed this by declaring her a saint one day before the 19th anniversary of her death.
About 1,500 homeless people from across Italy were bused into the Vatican to be given seats of honor at the Mass - and be served a pizza lunch by nuns afterward.
Pope Francis had in March announced that Mother Teresa, who spent 45 years serving the poor and sick on the streets in Kolkata, will be elevated to sainthood after the Church recognised two miracles attributed to her after her death.
Nuns from Teresa's Missionaries of Charity are active in the Ugandan capital. So far, Pope Francis has focused in society's outcast and most marginal, such as refugees, prostitutes, prisoners and homeless.
Mother Teresa of Calcutta has finally been given the Catholic Church's highest honor, as she was declared Saint.
Pope Francis on Sunday proclaimed Mother Teresa of Kolkata a saint, hailing her as the personification of maternal love and a powerful advocate for the poor.
1948: Permitted to leave her order and moves to Kolkata's slums to set up her first school. She founded the Missionaries of Charity group, whose influence spread to over 130 countries and included of over 4,000 sisters who helped run soup kitchens all over the world. She was firmly opposed to abortion, and she espoused the Catholic Church's belief that contraception is a sin.
She died September 5, 1997, and was beatified just six years later by St. John Paul II on October 19, 2003. Also, the senior sister t the Mother House, Mary Lysa said, "It's a day of rejoicing, a day of gratitude and a day of many, many blessings".
According to CatholicNews.org.uk, the Year of Mercy offers Catholics the opportunity to reflect on how we might better radiate and reflect the tender love of God in our world and to seek to draw others into experiencing that love and mercy. Besra spoke with CNN and commented about her miracle.
A picture of her as someone who was just as comfortable flying around in a private plane as clutching the hand of a dying patient has also emerged to counterbalance her saintly image.
A nun holds a photo of Mother Teresa before the start of the canonisation ceremony in St Peter's Square at the Vatican. Surely to them Mother Teresa must be a saint?
Allen again: "Few Catholic figures ever, and probably none in her own time, better illustrated that drive to make mercy concrete than Mother Teresa, from her AIDS hospices and soup kitchens to her homes for lost children and refugees". Some citizens believed that Mother Teresa cast a "shadow" over Kolkata's great past, history and opportunities, highlighting only the "bad parts" of the city.
Security fears in the wake of Islamic State (Isis) attacks in Europe meant only 100,000 tickets were issued for the mass, compared to the 300,000 in attendance for Mother Teresas beatification in 2003.
She is credited with healing an Indian woman from stomach cancer in 1998 and a Brazilian man from a brain infection in 2008.
Mother Teresa was awarded the Nobel peace prize in 1979.