| Regimental number | 1002 |
| Place of birth | Westport, New Zealand |
| Religion | Church of England |
| Occupation | Chemist |
| Address | Hare Street, Kalgoorlie, Western Australia |
| Marital status | Single |
| Age at embarkation | 19 |
| Next of kin | Father, J P Hallahan, Hare Street, Kalgoorlie, Western Australia |
| Enlistment date | |
| Rank on enlistment | Lance Corporal |
| Unit name | 11th Battalion, Headquarters |
| AWM Embarkation Roll number | 23/28/1 |
| Embarkation details | Unit embarked from Fremantle, Western Australia, on board Transport A11 Ascanius on |
| Rank from Nominal Roll | Corporal |
| Unit from Nominal Roll | 11th Battalion |
| Fate | Returned to Australia |
| Family/military connections | Brother: 503 Sergeant Walter Rewi HALLAHAN, 11th Bn, killed in action, 18 September 1918. |
| Other details |
War service: Egypt, Gallipoli, Western Front Medals: 1914-15 Star, British War Medal, Victory Medal |