These early versions of the hymn, though, did not use the melody familiar to everyone today. That melody was common in early America under the name "New Britain" or sometimes titles like "Harmony Grove" and, oddly, "Amazing Grace." The authorship of the melody is lost to history, but we do know that the adapting of Newton's text to the "New Britain" melody occurred in 1855; a colorful song leader and evangelist named William Walker ("Singing Billy") put it in his widely used songbook Southern Harmony. From there it quickly became a part of hundreds of church repertoires.
The song got into an even broader range of popular culture when it became a favorite of the folk revival movement in the 1960s. It appeared in the popular film Alice's Restaurant and as a hit single by folksinger Judy Collins. Then, in 1972, the Royal Scots Dragoon Guards made a recording of it featuring bagpipes, and it became a surprise hit, both in England and the United States. The recording helped establish a tradition of pipers playing it at political or military funerals, and at the services for policeman killed in the line of duty. http://www.pbs.org/americanrootsmusic/pbs_arm_es_religious.html
Amazing Grace at funerals
The song got into an even broader range of popular culture when it became a favorite of the folk revival movement in the 1960s. It appeared in the popular film Alice's Restaurant and as a hit single by folksinger Judy Collins. Then, in 1972, the Royal Scots Dragoon Guards made a recording of it featuring bagpipes, and it became a surprise hit, both in England and the United States. The recording helped establish a tradition of pipers playing it at political or military funerals, and at the services for policeman killed in the line of duty.
http://www.pbs.org/americanrootsmusic/pbs_arm_es_religious.html