Andrew Corsini was born in Florence on 30 November 1302 into noble and illustrious Corsini house; he was born as one of twelve to Nicholas Corsini and Peregrina (some sources suggest Gemma) degli Stracciabende. One brother was Tommaso. Upon his birth he was named in honor of the apostle of that name for he was born on his feast. His parents - while he was still in the womb - placed him under the protection of the Blessed Virgin.
He was once wild and dissolute before he heard the call from the Lord and decided to consecrate himself to Him. Extravagance and vice were normal to him and it pained his devout mother. Once he prepared for a banquet and expressed himself in a disrespectful manner to his mother which moved her to tears. He cared little for that until she told him she saw him as a wolf among sheep in her dream confiding that she hoped he would convert from his wicked mannerisms. This made a profound impression on him and he set out at once for the Santa Maria del Carmine church to reflect where he resolved then and there to become a friar. He joined the Carmelites in Florence in 1318 for his novitiate and began a life of great mortification. His ordination to the priesthood was celebrated in 1328. Corsini's parents prepared music and a banquet for his ordination but he retreated to a little convent on the town's outskirts to celebrate his first Mass in relative peace. Corsini began preaching in Florence before he was sent for his studies in both Paris (at the college) and Avignon. He resided in Avignon with his cousin Cardinal Pietro Corsini. He returned to Florence in 1332 and was chosen as the prior for his convent.
Upon his return he became known as the "Apostle of Florence" and he was regarded as a prophet and a wonderworker. In 1348 as the Black Plague was prevalent in area he was appointed as the order's Tuscan Provincial during the General Chapter meeting in Metz. On 13 October 1349 a papal bull from Pope Clement VI appointed him as the Bishop of Fiesole and he hid himself upon learning of this appointment where he despaired. The inscription on his tomb states that "he was snatched from the Carmel to the church and the miter of Fiesole". This perhaps gave rise to the legend that he fled but that a child discovered him at the charterhouse at Enna and later accepted the nomination as bishop as the result of a vision.
He redoubled his austerities as a bishop (he wore a hair shirt and iron girdle as well as sleeping on a bed of vine-branches) and was lavish in his care of the poor; he was sought after as a peacemaker and this is most notable in Bologna where Pope Urban V (who learnt of his peacemaking abilities) sent him as a papal legate to heal the breach between the nobles and the people. The bishop kept six servants on hand and he appointed two vicars to aid him in governing his diocese. He also enforced discipline amongst the diocesan priests. Corsini tried to avoid discourse with women as much as possible and he kept a list of names of poor people so he knew who to visit and provide goods to in order to alleviate their suffering. On 28 March 1350 he issued an edict that regulated revenue to the poor "for the love of God" as he often said. On 1 June 1368 he consecrated the altar of the Figline Valdarno church.
It was reported that - in 1373 as he celebrated Midnight Mass on Christmas Eve - the Blessed Virgin appeared to him and told him he would leave this world on the Three Kings' feast. It came to pass as the vision had told him for he fell ill on Christmas night and he died as foretold. His remains were moved to Florence in the evening of 2 February 1373 and his remains were later found to be incorrupt upon exhumation in 1385. The location of his burial was damaged in 1771 but his remains were left undisturbed.