The Roman Catholic nun, known for her work with the poor and needy, will be canonised during a special mass at St Peter's Square in the Vatican after being judged to be responsible for two miracles.
In the eyes of the church, someone can only become a saint if they have two officially verifiable miracles attributed to them after their death.
An individual can only become a saint once they have died, and the process doesn't normally begin until at least five years after the death of the candidate.
This is to allow grieving to pass and the case to be examined without emotion.
|Mother Teresa's funeral|
However for others the wait is much shorter - Pope Benedict XVI waived the five year period for his predecessor John Paul II, in 2005 to begin his path to sainthood.
St John Paul II waived the normal five-year wait for Mother Teresa too.
Mother Teresa died in September 1997, at the age of 87 and her canonisation began just two years later. She will officially be made a saint exactly 19 years after her death. The Roman Catholic Church currently has more than 10,000 saints.
See the two miracles attributed to Mother Teresa after her death.
Mother Teresa's first 'miracle'
A Bengali tribeswoman Monica Besra was cured from an abdominal tumour thanks to Mother Teresa's intervention from heaven.
According to a commission from the Vatican, a locket containing a picture of the nun was placed on the patient's stomach.
Ms Besra said a beam of light emerged from the picture and relieved her of a cancerous tumour.
However, there is some controversy about the story.
Her doctor, Ranjan Mustafi, reportedly says she didn't have cancer and the tubercular cyst she did have was cured by prescription medicine.
Pope John Paul II accepted this first 'miracle' attributed to Mother Teresa as authentic five years after her death. This cleared the way for her beatification in 2003.
The second 'miracle'
This 'miracle' was given the nod by Pope Francis in 2015, which made her sainthood a formality.
Mother Teresa's intercession was said to have helped cure Brazilian man Marcilio Haddad Andrino of several brain tumours in 2008, according to the Vatican.
Mr Andrino from Santos and then 35, had been diagnosed with a viral brain infection resulting in multiple abscesses.
Treatments were said to be ineffective and he struggled to walk down the aisle at his wedding in September 2008.
By December he went into a coma.
Mr Andrido's new wife spent months praying to the 'saint of the gutter'.
Her family joined her in prayer as the apparently dying patient was taken to the operating theatre.
When the surgeon came into the room, he reportedly found the patient awake, pain free and asking "What am I doing here?"
Speaking ahead of Mother Teresa's official canonisation, Mr Andrino said he didn't feel special - but lucky. He said:
"If it hadn't happened to me maybe there would be someone else tomorrow. She did not distinguish. I don't feel special."
A Vatican medical commission voted unanimously in September 2015 that the healing was inexplicable.
A spokesman for the Vatican said:
"The Holy Father has authorised the Congregation for the Causes of Saints to proclaim the decree concerning the miracle attributed to the intercession of blessed Mother Teresa."All 100,000 tickets to the special mass on Sunday have been allocated, and more people are expected to line the streets around St Peter's Square for the service.