On the evening of September 13, 1935, St. Faustina Kowalska saw an angel come to chastise a city for its sins; she began to plead with the angel and offer Christ's body and blood for that city, and the angel could not act. The next morning, Christ taught her the words of what would become the Chaplet of Divine Mercy and instructed her to pray it on her rosary beads.

The Chaplet uses the same beads as the Rosary but a different set of prayers. On the large beads (where the Our Father falls in the Rosary), the prayer is: 'Eternal Father, I offer You the Body and Blood, Soul and Divinity of Your Dearly Beloved Son, Our Lord Jesus Christ, in atonement for our sins and those of the whole world.' On each of the ten small beads of each decade: 'For the sake of His sorrowful Passion, have mercy on us and on the whole world.'

Christ promised many graces to those who pray the Chaplet, especially at the hour of His death (3 PM) and for the dying. The Chaplet has been promoted heavily by John Paul II — himself a Pole who lived through the Polish history Faustina knew — and is now prayed worldwide.