St. Stanislaus was born son of a noble Polish senator at Rostkowo, Przasnysz County, Poland, on October 28, 1550. He attended the Viennese Jesuit college from age 14 with his brother Paul, who badly mistreated him. While staying at the home of a Lutheran, he became gravely ill, but was not allowed to call for a priest. He prayed to his personal patron, Saint Barbara, who appeared to him in a vision with two angels, and administered Communion. He was then cured from his disease by Our Lady who told him to become a Jesuit, though it was against his family’s wishes.
He entered the Society of Jesus in Rome on his 17th birthday on October 28, 1567. He attended the Jesuit college in Rome, Italy. He was a friend of Saint Peter Canisius and a student of Saint Francis Borgia. He died at Rome during the night of 14–15 August 1568.
Saint Stanislaus Kostka was brutally bullied by his brother and fled to Rome, to join the Jesuits at the Novitiate, where he died not long after. This painting, by Andrea Pozzo, is in the first of the rooms dedicated to Kostka's memory. (Source)
On the evening of his departure from this world, he wrote a letter to the Blessed Virgin begging her to call him to the skies there to celebrate with her the glorious anniversary of her Assumption. His confidence in the Blessed Virgin, which had already brought him many signal favours, was this time again rewarded; on August 15th, towards four in the morning, while he was rapt in pious utterances to God, to the saints, and to the Virgin Mary, he died.
Saint Stanislaus had drawn as his monthly patron for August the glorious martyr Saint Lawrence, and in his honour he performed daily some penance or devotion. On the eve of his feast, he obtained leave to take the discipline; in the morning he went to Communion, and then laid before the image of the saint a letter addressed to Our Lady, in which he begged that he might die on her Feast of the Assumption, and he prayed Saint Lawrence to present to her his petition. That night he was seized with a slight fever, which, however, rapidly increased; and on Assumption Eve, he received the last sacraments. Then, as he lay dying, he had brought to him a little book containing a litany in his own writing of his monthly patron saints, whom he constantly invoked. At 3 a.m. on the Feast of the Assumption, he face suddenly lit up with joy, and he breathed forth his soul to the Mother of God, who had come to conduct him to heaven (Source from Miniature Lives of the Saints by Bowden)