St. Catherine of Siena was born during the outbreak of the plague in Siena, Italy on March 25, 1347. She was the 25th child born to her mother, although half of her brothers and sisters did not survive childhood. Catherine herself was a twin, but her sister did not survive infancy. Her mother was 40 when she was born. Her father was a cloth dyer.
At the age of 16, Catherine's sister, Bonaventura, died, leaving her husband as a widower. Catherine's parents proposed that he marry Catherine as a replacement, but Catherine opposed this. She began fasting and cut her hair short to mar her appearance.
Her parents attempted to resist this move, to avoid marriage, but they were unsuccessful. Her fasting and her devotion to her family, convinced them to relent and allow her to live as she pleased. Catherine once explained that she regarded her father as a representation of Jesus and her mother as Our Lady, and her brothers as the apostles, which helped her to serve them with humility.
Despite Catherine's religious nature, she did not choose to enter a convent and instead she joined the Third Order of St. Dominic, which allowed her to associate with a religious society while living at home.
Fellow Dominican sisters taught St. Catherine how to read. Meanwhile, she lived quietly, isolated within her family home.
St. Catherine developed a habit of giving things away and she continually gave away her family's food and clothing to people in need. She never asked permission to give these things away, and she quietly put up with their criticisms.
Something changed her when she was 21. She described an experience she referred to as her "mystical marriage to Christ." There are debates over whether or not St. Catherine was given a ring with some claiming she was given a bejeweled ring, and other claiming the ring was made of Jesus's skin. St. Catherine herself started the rumor of the latter in her writings, but she was known to often claim the ring itself was invisible.
Such mystical experiences change people, and St. Catherine was no exception. In her vision, she was told to reenter public life and to help the poor and sick. She immediately rejoined her family and went into public to help people in need.
She often visited hospitals and homes where the poor and sick were found. Her activities quickly attracted followers who helped her in her mission to serve the poor and sick.
St. Catherine was drawn further into the world as she worked, and eventually she began to travel, calling for reform of the Church and for people to confess and to love God totally. She became involved in politics, and was key in working to keep city states loyal to the Pope. She was also credited with helping to start a crusade to the Holy Land. On one occasion, she visited a condemned political prisoner and was credited with saving his soul, which she saw being taken up to heaven at the moment of his death.
St. Catherine allegedly was given the stigmata, but like her ring, it was visible only to herself. She took Bl. Raymond of Capua has her confessor and spiritual director.
From 1375 onwards, St. Catherine began dictating letters to scribes. She petitioned for peace and was instrumental in persuading the Pope in Avignon to return to Rome.
She became involved in the fractured politics of her time, but was instrumental in restoring the Papacy to Rome and in brokering peace deals during a time of factional conflict and war between the Italian city states.
She also established a monastery for women in 1377 outside of Siena. She is credited with composing over 400 letters, her Dialogue, which is her definitive work, and her prayers. These works are so influential that St. Catherine would later be declared a Doctor of the Church. She is one of the most influential and popular saints in the Church.
By 1380, the 33-year-old mystic had become ill, possibly because of her habit of extreme fasting. Her confessor, Raymond, ordered her to eat, but she replied that she found it difficult to do so, and that possibly she was ill.
In January of 1380, her illness accelerated her inability to eat and drink. Within weeks, she was unable to use her legs. She died on April 29, following a stroke just a week prior.
St. Catherine's feast day is April 29, she is the patroness against fire, illness, the United States, Italy, miscarriages, people ridiculed for their faith, sexual temptation, and nurses.
Sources:
https://en.wikipedia.org/wiki/Catherine_of_Siena
https://www.catholic.org/saints/saint.php?saint_id=9