The personal pilgrimage of Pope John Paul II in 1979, commemorating the centenary of the apparition, inspired an even greater devotion to the Shrine and endorsed the indelible seal of Vatican approval. Mother Teresa of Calcutta visited the Shrine in June of 1993. One and a half million pilgrims visit the Shrine annually.

On the wet Thursday evening of the 21st August, 1879, at about the hour of 8 o'clock, Our Lady, St. Joseph, and St. John the Evangelist appeared in a blaze of Heavenly light at the south gable of the Church of St. John the Baptist. Behind them and a little to the left of St. John was a plain altar. On the altar was a cross and a lamb with adoring angels. The Apparition was seen by fifteen people one of whom was a thousand metres from the church at the time. The ages of the witnesses ranged from six years to seventy-five and included men, women, teenagers and children.

The poor humble witnesses at first thought that the priest had bought new statues for the chapel, but since they had heard nothing of this, decided to look more closely. As they approached the church, they realized that these were not statues because they were moving. They were seeing Our Lady. The witnesses distinctly beheld the Blessed Virgin Mary clothed in white robes with a brilliant crown on her head. Over the forehead where the crown fitted the brow, she wore a beautiful full-bloom golden rose. She was in an attitude of prayer with her eyes and hands raised towards Heaven. St. Joseph stood on Our Lady's right. He was turned towards her in an attitude of respect. His robes were also white. St. John was on Our Lady's left. He was dressed in white vestments and resembled a bishop, with a small mitre. He appeared to be preaching and he held an open book in his left hand.

The witnesses watched the Apparition in pouring rain for fully two hours, reciting the Rosary. Although the witnesses standing before the gable were drenched, no rain fell in the direction of the gable. They felt the ground carefully with their hands and it was perfectly dry as was the gable itself.

A Commission was set up within six weeks of the Apparition by Most Rev. Dr. John MacHale, Archbishop. Fifteen witnesses were examined and the Commission reported that their evidence was "trustworthy and satisfactory". The Report was published in the newspapers and immediately pilgrims began to flock from all parts of the country and overseas. The sick and disabled were taken along in great numbers and hundreds of cures were reported in the public Press of that time. One of the first organised pilgrimages to Knock Shrine came from Limerick and they were received and welcomed at Tuam by Most Rev. John MacHale. A second Commission was established in 1936 while three of the official witnesses were still alive. They confirmed the evidence they had given in 1879. One of the witnesses was Mrs. O'Connell (nee Mary Byrne). She confirmed her evidence, on her death-bed, under oath and added "I am perfectly clear about everything I have said and I make this statement knowing I am about to go before my God". She died six weeks later. The verdict of this Commission was that the evidence of the witnesses was "upright and trustworthy."