Mother Teresa, an Albanian nun who won the Nobel Peace prize in 1979, is best known for her work among the poor in the slums of Kolkata (formerly Calcutta), India.
The Pope has approved the healing of a Brazilian man with brain tumours who prayed to Mother Teresa.
Pope Francis has been dedicated to ministering to the poor in similar ways to Mother Teresa and is a great supporter of her work. During a visit to Albania in 2004, Pope Francis told his interpreter he was impressed by her fortitude but also in some ways feared it.
Francis met Mother Teresa in 1994 at a Vatican synod.
A spokesperson, Revd Federico Lombardi at the Vatican, said the Pope, then the Archbishop Jorge Mario Bergoglio, developed a great esteem for her: "He heard her intervene often with great strength, without letting herself in any way be intimidated by an assembly of bishops. And from that he developed a great esteem for her, as a strong woman, a woman able to give courageous testimony."
Premier's Cindy Kent met Mother Teresa:
After the service a group of journalists were invited to meet with her.
It was a very small room and she was sitting in the corner. She looked very diminutive and frail and yet there had been an amazing power when she'd spoken earlier.
I was quite near her, kneeling with my microphone.
She asked for a glass of water - and I got it for her.
She made the sign of the cross before drinking it - which a lot of people do before they eat a meal.
It made me realise that where she came from water is a very precious commodity.
I got her to sign her name for me - and it's something I will always treasure.
In Catholicism, two miracles are needed to become a saint.
The Vatican recognised Mother Teresa's first miracle in 2002, a healing of a Bengali tribal woman with an abdominal tumour.
She was beatified by Pope John Paul II in 2003, the first step to being canonised.
The celebration of Mother Teresa's sainthood is expected to take place in Rome on September 4, which will be part of the Pope's Jubilee year of mercy.
Mother Teresa, nicknamed the "Saint of the Gutters" died in Kolkuta in 1997 at the age of 87.
Canon John O'Toole once met the Nobel Peace Prize winner and told Premier's News Hour she was a special person.
He said: "I still recall, it was in the early 70s, and my memory is she was a small woman in a large cathedral.
"But it was obvious she had an enormous heart and the simplicity and humility was evident."
Canon John O'Toole speaking to Premier's Hannah Tooley:
By Megan Howe.