The world-famous apostle of the Divine Mercy was born on 25 August 1905 in the village of Głogowiec, in the Świnice Warckie parish (abour 50 km outside the city of Łódź) as the third of ten children in the family of Marianna and Stanisław Kowalski. She attended school for less than 3 years. Subsequently, she worked as a charwoman in the households of well-to-do families in Aleksandrów Łódzki, Łódź and Ostrówek in the Klembów county near Warsaw. On August 1 1925, when she was 20 years old, she joined the Congregation of the Sisters of Our Lady of Mercy. In the course of the 13 years she had spent in the Congregation, she stayed in a number of its houses: in Cracow (the longest), Vilno, Płock and Warsaw where she worked as a cook, gardener and gatekeeper. She suffered from tuberculosis of the lungs and of the alimentary canal. She also experienced great spiritual tribulations, as she had offered her life in sacrifice for poor sinners, particularly those who faced the prospect of being deprived of the grace of salvation. Sr. Faustina's life, which at first glance seems so grey and monotonous was filled with an extraordinary depth of mystical life. She was endowed with many extraordinary graces, among others with the gift of contemplation, concealed stigmata, bilocation, the gift of prophecy, of being able to read human souls, and of mystical betrophal and nuptials all of which enabled her to attain the heights of unity with God on earth. Years of her monastic life were full of special graces: revelations, visions, hidden stigmas, the participation in Jesus agony, the gift bilokation, of reading in the human spirits, the prophecy or the gift rarely met of the mystical betrothal and nuptials. Living contact with God, the Most saint Mother, angels, saints, with the souls in purgatory - entire preternatural world was for her not less real and real than the one which she discerned with senses. In spite of such great giving special graces she knew that not they were being sacred.
In the Diary she wrote: neither graces nor revelations nor admirations for it [for soul] do not make her excellent, but internal uniting my soul with God. These gifts are only an ornament for soul, but not a content. The Holiness and my excellence consist on dense uniting my will with the will of God (Dz. 1107
The mission of the Blessed Sr. Faustina has been recorded in her Diary which she had kept at the specific request of the Lord Jesus and her confessors. In it, she recorded faithfully all of the Lord Jesus' wishes and also described the encounters between her soul and God. Secretary of My most profound mystery, know that yours is an exclusive intimacy with Me. Your task is to write down everything that I make known to you about My mercy, for the benefit of those who by reading these things will be comforted in their souls and will have the courage to approach Me (Diary 1693). In an extraordinary way, Sr. Faustina's work sheds light on the mystery of the Divine Mercy. It delights not only the simple and uneducated people, but also scholars who look upon it as an additional source of theological research. The Diary has been translated into many languages, among others, English, German, Italian, Spanish, French, Portugese, Russian, Hungarian, Czech, and Slovak. Faustyna sister destroyed with illness and different suffering which she carried as the voluntary sacrifice for sinners, fully seen intellectually and mystical united with God died in Cracow on 5 October 1938 being only 33 years old. The fame of the holiness of her life grew together with widening in church services to the God's Mercy and graces wheedled by her intercession. In 1965-67 in Cracow an information process concerning the life and virtues for her was carried and in 1968 in the Rome a beatification process which was finished was begun in December of 1992. On 18 April 1993, in Piotr's Święty Square in the Rome, Holy Father John Paul II accomplished the act of her beatification, and 30 April 2000 of its canonization. Her relics are resting in the sanctuary of the God's Mercy in Cracow-Łagiewniki.
The Lord Jesus chose Sr. Faustina as the Apostle and "Secretary" of His Mercy, so that she could tell the world about this great message: In the Old Covenant I sent prophets wielding thunderbolts to My people. Today I am sending you with My mercy to the people of the whole world. I do not want to punish aching mankind, but I desire to heal it, pressing it to My Merciful Heart (Diary 1588) - the Lord Jesus told Sr. Faustina. (Dz. 1588). 
The mission of the Blessed Sr. Faustina consisted in 3 tasks: 
Reminding the world of the truth of our faith revealed in Holy Scripture about the merciful love of God towards every human being. 
Entreating God's mercy for the whole world, among others through the practice of new forms of devotion to Divine Mercy, such as the veneration of the image of the Divine Mercy with the inscription: Jesus, I Trust in You, the feast of the Divine Mercy celebrated on the first Sunday after Easter, chaplet of the Divine Mercy, prayer at the Hour of Mercy (3 p.m.) and spreading the devotion to the Divine Mercy. 
Initiating the apostolic movement of the Divine Mercy which undertakes the task of proclaiming and entreating God's mercy for the world and strives for perfection in the spirit of childlike confidence in God, expressed in the fulfillment of His will and the attitude of mercy towards one's neighbor.