The Divine Mercy Chaplet came from revelations made to Sister Maria Faustina Kowalska in the 20th Century.
From divinemercy.org: Sister Faustina was a young, uneducated nun in a convent of the Congregation of Sisters of Our Lady of Mercy in Poland during the 1930s. She came from a poor family that struggled during the years of World War I. She had only three years of simple education, so hers were the humblest tasks in the convent, usually in the kitchen or garden. However, she received extraordinary revelations — or messages — from our Lord Jesus. Jesus asked Sr. Faustina to record these experiences, which she compiled into notebooks. These notebooks are known today as the Diary of Saint Maria Faustina Kowalska, and the words contained within are God’s loving message of Divine Mercy.
Jesus said to Sister Faustina:
‘Say unceasingly this chaplet that I have taught you. Anyone who
says it will receive great Mercy at the hour of death. Priests
will recommend it to sinners as the last hope. Even the most
hardened sinner, if he recites this Chaplet even once, will
receive grace from My Infinite Mercy. I want the whole world to
know My Infinite Mercy. I want to give unimaginable graces to
those who trust in My Mercy… . ‘
‘… . When they say this Chaplet in the presence of the dying, I
will stand between My Father and the dying person not as the just
judge but as the Merciful Savior’.
Now, here is a video on how to say it as we recite it as often as we are able in order to plead from mercy from our Lord and Savior:
+JMJ+
†The Ecu-Men† 