Little is known about the personal life of  James Kiernan, other than that he was born in Wollongong, NSW, to Mrs. Catherine Tiernan and her husband, Patrick, who had been dead for six years before James enlisted for World War 1. James was a metal worker, 20 years and 8 months old, 5' 3" tall and married Elsie Toy Kiernan in 1916. She was then living in Melbourne at 52 Collins Place, moving then to 53 Victoria Parade, East Melbourne. She died  on June 26, 1917; the couple had been married only one year. The only other person in his life was his Aunt,  Mrs. S. Johnson, who claimed that she 'had reared the boy' and he had wanted her to have financial support from him as a result.

James Tiernan enlisted at the Sydney Town Hall. He had already had two years service in the militia, and one year in Home Defence with the 28th Infantry, City of Sydney. He enlisted on 19 January, 1916, and trained with A Company, 18th Battalion from 31st January to 29th January, 1916. From there he went  for further training with the 6th Reinforcements, 31st Battalion, from 16 April, 1916 and embarked for England on 18 August 1916 on board HMAT A17 Port Lincoln.

Once in England, he was placed with the 57th Battalion AIF, marching in on 10 September, 1916, and embarking for France on 15 September. At this stage, it appears that he was placed temporarily with the 59th Battalion, perhaps on the move from Britain to France.. He finally marched out to join the battlefront and was taken on strength with the 57th Battalion on 30 September, 1916. 

The battle of Fromelles, beginning 19th July, had been a disasater for thev AIF. Fortunately, the 57th battalion had only a supporting role, but this meant that in the following months, they were one of the units which had the task of holding the line against the German army for two months afterwards. This is when James Kiernan would have joined them.

He served in the trenches for perhaps six weeks, before catching influenza. He was taken off the field by the 14th Field Ambulance, then to hospital in Etaples on 24 November, 1916. After two weeks in hospital, where he was identified as having 'slight tachycardia' he was assigned to the 5th Australian Division Base Depot at Etaples. Here he would have been subject to further tests,medical checks and at least ten days of extra training. James Tiernan was here for some time, then left for England on 11 April, 1917. On 28 August, he returmed to France from Southampton, but almost immediately,  was infected with another bout of influenza. He was back in hospital from 14 September , 1918,  Taken from the battlefield by the 15th Field Ambulance and placed in the 1st Australian General Hospital in Rouen. On 13 October, he was moved to the 2nd General Hospital at Havre, and from there to the  the Australian Base Depot. On 27-28th November, he was in revovery mode and went AWOL at Havre, earning him 14 days forfeiture of pay. He finally rejoined the 57th Battalion when the war had finished, marching out ot join his unit on 7 March, then marching in to Base Depot on 23 March.

James Tiernan, and presumably the rest of the 57th Battalion, was sent home on board the Orontes on 1  July, 1919. He was discharged from further service on 15 August, 1919. In 1928, he was living at 22 Rainbow St., Redfern, NSW, which would have been close to his aunt, and perhaps mother. In 1930, he was living in Paddington, NSW, and working as a labourer. He is probably the James Tiernan who died on 12 June, 1931, and was buried at Rookwood Cemetery, Rookwood, NSW. He would have been 36 years old.