| Regimental number | 1639 |
| Religion | Roman Catholic |
| Occupation | Mental attendant |
| Address | Perth, Western Australia |
| Marital status | Single |
| Age at embarkation | 28 |
| Next of kin | Father, Hugh O'Brien, Mill Street, Carrick-on-Suir, Tipperary, Ireland |
| Enlistment date | 15 September 1915 |
| Date of enlistment from Nominal Roll | 8 September 1915 |
| Rank on enlistment | Private |
| Unit name | 10th Light Horse Regiment, 12th Reinforcement |
| AWM Embarkation Roll number | 10/15/2 |
| Embarkation details | Unit embarked from Fremantle, Western Australia, on board HMAT RMS Mongolia on 22 November 1915 |
| Rank from Nominal Roll | Bombardier |
| Unit from Nominal Roll | 11th Field Artillery Brigade |
| Fate | Returned to Australia 9 December 1918 |
| Family/military connections | Brothers: 106 Lance Corporal Rufus Hugh O'BRIEN, 44th Bn, returned to Australia, 25 January 1919; 982 Pte Thomas O'BRIEN, 44th Bn, returned to Australia, 17 June 1918. |
