The tribute marks the spot where Newton began his conversion to Christianity when coming ashore after surviving a near-shipwreck.
“It was at a very crucial point in his life," Ruth Garvey-Williams, secretary of the Amazing Grace Initiative told NewsLetter.co.uk.
“Up until that point he was self-described as a wretch. He was involved in the slave trade.
“He was travelling to Liverpool from Africa, and because of the trade winds they had a very circuitous route.
“He was caught in a violent storm, and found himself crying out for mercy. He thought: ‘what mercy can there be for me, a wretch?’”
The ship managed to make it to safety, but Newton "stepped ashore a changed man." Even though he remained active in the slave trade for another six years, he later became a staunch opponent of the industry.
Garvey-Williams said the idea for the platform, with a mosaic design incorporating the words "Amazing Grace" and the image of the ship, The Greyhound, began in 2006 after Amazing Grace Initiative member Mike Mullins read about Newton’s remarkable story.
The €30,000 project was paid for by the Inishowen Development Partnership using European funding, and by Buncrana Town Council.
DUP’s Jonathan Bell and Sinn Fein’s Martin McGuinness attended the site's launch, where Inishowen Gateway Singers gave a rendition of Newton's famous hymn.
“It is extraordinary to think that John Newton’s safe delivery to these shores at Buncrana on that fateful night of April 8, 1748 inspired him to write one of the most well-known and best-loved hymns in the world," said Stormont junior minister Bell.
McGuinness said: “As one of the world’s best-known hymns, ‘Amazing Grace’ has worldwide appeal that will draw people to this beautiful part of Ireland, where John Newton started his spiritual journey.”
Irish group Celtic Woman sings "Amazing Grace":