| Regimental number | 53259 |
| Date of birth | |
| Place of birth | Orawia |
| Religion | Roman Catholic |
| Occupation | Farmer |
| Marital status | Single |
| Age at embarkation | 24.2 |
| Height | 5' 7" |
| Weight | 150 lbs |
| Next of kin | Brother, Bryan F O'Brien, Orawia |
| Previous military service | Served in 7th Mounted Regiment, Territorial Force; still serving at time of NZEF enlistment. |
| Enlistment date | |
| Rank on embarkation | Private |
| Unit name | New Zealand Expeditionary Force, 27th Reinforcements (First Draft), Otago Infantry Regiment, D Company |
| Embarkation details | Unit embarked from Wellington on board HMNZT 87 Tahiti on |
| Final rank | Private |
| Final unit | 1st Battalion, Otago Infantry Regiment |
| Fate | Killed in Action |
| Age at death from cemetery records | 24 |
| Place of burial | No known grave |
| Commemoration details | Tyne Cot Memorial (New Zealand Apse, Panel No 3), nr Ieper, Belgium |
| Miscellaneous information from cemetery records | Parents: Morgan and Catherine O'Brien (both b. Ireland), Makarewa, Southland, Invercargill. Native of Orawia, Southland |
| Other details |
War service: Western Front Embarked Wellington, 12 June 1917; disembarked Devonport, England, 16 August 1917, and marched into Sling Camp. Proceeded overseas to France, 23 September 1917; joined 1st Bn, Otago Infantry Regiment, in the field, 7 October 1917. Killed in action, 12 October 1917. Medals: British War Medal, Victory Medal |
| Sources | Nominal Roll Vol. 3: Roll 67, p. 21 Archives New Zealand (Wellington), Agency AABK, Series 18805, File 21381489 |