1747 – John Newton, a sailor on a slave ship, is converted to Christianity during a huge storm at sea. He eventually becomes an Anglican clergyman, the author of the famous hymn “Amazing Grace” and a zealous abolitionist.
http://www.christianhistoryinstitute.org/today/03/10
The greatest influences in the 19th century that propelled „Amazing Grace” to spread across the U.S. and become a staple of religious services in many denominations and regions were the Second Great Awakening and the development of shape note singing communities.