Harry Cattanach was the son of Henry James Goodrich Cattanach (1833-1911) and his wife, Sarah, nee Smith. He was one of nine children born to the couple: Christina (b.1864), Sarah (b.1865), Jane (b.1967), Harriet (b.1871), Victoria (b.1873), Harry (b.1875), Adam (b.1877), Anne (b.1879) and Maud (b.1882). He enlisted on 31 August, 1914 at Dimboola, Victoria, where he had been farming, claiming to be 34 years old; in fact, he was by then nearly forty. He was placed in the 8th Battalion AIF, 2nd Division. After training, they sailed from Melbourne on 19 October, 1914, on board HMAT Benalla A24, disembarking in Egypt on 2 December. 

The 8th Battalion was one of the first infantry battalions raised in Victoria. After further training, they  took part in the Gallipoli landing at Anzac Cove, as part of the second wave.  Harry Cattanach was one of those wounded as they reached the beach on 25 April, 1915. He suffered a gunshot wound to his right thigh, a shrapnel wound to his left thigh and loss of teeth from both upper and lower jaw as a result of dirt thrown up by shelling. 

His record from then on is one of suffering. He was first taken on board HMHS Ionian, where he remained from 26 April-2 May. He was then moved to the No.5 Indian Hospital at Alexandria, from 2 May- 1 June. From here, he was sent to the No.15 General Hospital at Alexandria, 1 June -19 June, then onto HMS Varvasa, 19 June - 1 July, and then to four different hospitals in England: Manchester 1 July - 15 July; Shelford 15 July - 8 August; Harefield     Park, Derham, to the No. 1 Australian Auxiliary Hospital, 8 August - 1 October. At this stage, he had been forty days under treatment after only two days active service. He went to Epsom 1 October - 6 October, 1915 and was then sent to the Woodside Park Military Convalescent Hospital. 

His injuries were recorded by three separate boards of medical inquiry, two in England and one back in Melbourne. The origin of his injuries were described as: On 25 April, 1915,  at Gallipoli, struck by shrapnel on left thigh and by rifle bullet on outer side of the right thigh, exit wound on inner side, hospital 4 1/2 months. Extensive scarring of left thigh and marks of bullet wounds on right thigh - has lost the use of 3 toes on right foot - complains of numbness and pain in left thigh and difficulty in walking. It was decided that he was not able to continue in active service, but could be fit enough to undertake home service.

Harry Cattanach was returned to Australia on board HTS Runic A54, leaving from Portland, England, on 7 November, 1915 and arriving back in Melbourne on 22 December, 1915. On 17 January,  he was examined at Melbourne Hospital. His report stated: No more military service, but injury not permanent, massage and exercise to the muscles of the leg. Total incapacity to earn a living at present. Not fit to be discharged to earn a living. On 8 May, a further report: Returned Runic 12/12/15. has been having massage daily since. Will be paraded before O.C. on 28/3/16 and be transferred to Strathallen on 29/3/16. he should almost be fit for discharge to duty. on 13 September, Harry Cattanach was discharged as medically unfit and was given a war pension. He returned to live at  115 George St., with his mother and sisters. By 1909, the family had moved to 55 Gipps St, East Melbourne, with the Electoral Roll listing Harry James, an agent; Harry James, a clerk; Sarah, home duties and Sarah Smith, a governess.

Harry Cattanach died on 23 November, 1925, aged fifty, at Ultimo, Victoria.

His brother, Adam, enlisted on 22 March, 1916, serving with the 59th Battalion until 1918.  Another Henry James Goodricke Cattanach also enlisted in the AIF, on 27 Decmeber, 1915, and served with the 33rd Battalion, returning in 1919. He was probably a cousin, the son of Henry James Drummond Cattanach and his wife, Arabella McIntosh. This Henry was aged only 24 when he enlisted, over ten years younger that the East Melbourne Cattanachs, but like the other two Cattanachs was Presbyterian by religion.