| Regimental number | 443 |
| Place of birth | Sydney, New South Wales |
| School | State schools at Bega and Casino, New South Wales |
| Other training | Clerical and driving |
| Religion | Roman Catholic |
| Occupation | Stock and station agent |
| Marital status | Single |
| Age at embarkation | 29 |
| Next of kin | Father, Major W.E. O'Brien, Casino, New South Wales |
| Previous military service | Member of the NSW [Mounted?] Rifles. |
| Enlistment date | |
| Rank on enlistment | Private |
| Unit name | 6th Light Horse Regiment, C Squadron |
| AWM Embarkation Roll number | 10/11/1 |
| Embarkation details | Unit embarked from Sydney, New South Wales, on board HMAT A29 Suevic on |
| Rank from Nominal Roll | Private |
| Unit from Nominal Roll | 2nd Light Horse Regiment |
| Fate | Killed in Action |
| Place of death or wounding | Gallipoli, Turkey |
| Age at death | 27 |
| Age at death from cemetery records | 27 |
| Place of burial | Shell Green Cemetery (Plot II, Row K, Grave No. 6), Gallipoli, Turkey |
| Panel number, Roll of Honour, Australian War Memorial | 5 |
| Miscellaneous information from cemetery records | Parents: William and Mary O'BRIEN, 22 Crown Street, St. Peter's Sydney. Native of Sydney |
| Family/military connections | Cousin: John Broderick who was killed in action at Gallipoli. |
| Other details |
War service: Egypt, Gallipoli Medals: 1914-15 Star, British War Medal, Victory Medal |