William Ruddick was a former News Letter reporter who was orphaned at the age of five when his father who was a deck engineer on the Titanic, lost his life on the Titanic.
On the Titanics maiden voyage she struck an iceberg in the north Atlantic sailing from Southampton to New York. It sank on April 15, 1912, Killing 1,517 people in one of the worst peacetime maritime disasters in history.
Mr Millar was orphaned as his mother had died in January 1912.
The author of Stirabout, When Johnny Comes Marching Home and The Land Girlwas raised in Fool's Haven Cottage in the Co Antrim village of Boneybefore in Carrickfergus following his father's death.
The plaque was unveiled at the cottage where he was raised by his great aunt.
Ms Millar the of Mr Millar, herself a journalist, said in spite of her grandfather's dire start, "he went on to live a very successful life".
By the age of 18, one of Ruddick Millar's plays was being performed at the Grand Opera House in Belfast.
He continued to write plays for stage and radio, newspaper articles and books until his death aged 46 in 1952.
Ms Millar said her grandfather's account of his father "sailing away on Titanic and how he found out about the sinking as he sailed his own paper boat in the stream at Boneybefore has provided one of the fullest depictions of the effect of Titanic's loss on an ordinary family".
The story has since been re-written by Ms Millar in the book The Two Pennies.
She said: "The Millar family is delighted that my grandfather has been recognised in this way more than 50 years after his death.
"His writings portrayed a slice of Ulster life in the 1930s as well as capturing the deep sense of loss after the Titanic's sinking.
"He was the only author in the 1930s who was talking and writing about Titanic."
Mr Millar's daughter Gillian was among family members who attended the unveiling.
The plaque was unveiled by Northern Ireland representative of the Maritime Heritage Committee, Alliance councillor Sean Neeson.
Also in attendance were Belfast Titanic Society president John M Andrews and chairman Una Reilly MBE.
Ms Millar said: "My Aunt Gillian was able to tell us tales this morning about my grandfather's parties.
"Even though he had such a terrible start to life, he had a good sense of humour throughout and he made the best of it."