Mr John Joseph Kiernan was born in Fostragh, Ballinamuck, Co Longford, Ireland on 24 October 1885.

He was the son of John Kiernan (b. 1840), a farmer, and Catherine Kelleher (b. 1843) who had married around 1867. 

One of ten surviving siblings born to his parents, from a total of eleven, his known siblings were: Mary (b. 3 May 1868), Anne (b. 3 June 1870), Bridget (b. 30 October 1872), Catherine (b. 18 January 1875), Bernard (b. 17 May 1880), Margaret (b. 19 August 1883), Philip (b. 24 January 1890) and Ellen (b. 24 April 1894).

John appears on the 1901 census living with his family at house 2 in Fostragh, Ballinamuck. Aged 15, he had already left school and was working on his father's farm. 

He later emigrated to the USA, arriving in New York on 4 May 1904 aboard Umbria and destined to the home of his sister Margaret at 287 4th Street in Jersey City, New Jersey. He appears on the 1910 census living with his another sister Catherine Tierney and her large family in Jersey City. Whilst there he worked as a barman for his maternal uncle Philip Kelleher (b. 1855), a widower, in one of his establishments at 268 Varick Street, Jersey City.

John returned home to Ireland in August 1911 to visit family. For his return to New Jersey he would be accompanied by his younger brother Philip and they were also travelling with a crowd from their area in Co Longford that included the Murphy sisters, Catherine and Margaret, and Thomas McCormack, who was apparently a cousin. 

John boarded the Titanic at Queenstown on 11 April 1912 as a third-class passenger (ticket number 367227, which cost £7, 15s). It is believed he shared a cabin with his brother and Thomas McCormack.

On the night of the sinking, John, after encountering difficulties getting to higher decks, escorted the Murphy sisters to a lifeboat, reportedly giving Margaret his lifebelt as she did not have one.

John Kiernan died in the sinking, and his body, if recovered, was never identified. His brother was also among the lost.

It was later reported that Margaret Murphy and John Kiernan were sweethearts intent on marrying once they reached America. Margaret sued the New York Press for libel.