| Regimental number | 421 |
| Place of birth | Sale Victoria |
| School | State School, Victoria. |
| Other training | Nil |
| Religion | Baptist |
| Occupation | Labourer |
| Address | Thompson Street, Sale, Victoria |
| Marital status | Single |
| Age at embarkation | 21 |
| Next of kin | Mother, Mrs M Costello, Gerangamete PO, Gerangamete, Victoria |
| Previous military service | Nil |
| Enlistment date | |
| Rank on enlistment | Private |
| Unit name | 39th Battalion, B Company |
| AWM Embarkation Roll number | 23/56/1 |
| Embarkation details | Unit embarked from Melbourne, Victoria, on board HMAT A11 Ascanius on |
| Rank from Nominal Roll | Private |
| Unit from Nominal Roll | 39th Battalion |
| Fate | Killed in Action |
| Miscellaneous details (Nominal Roll) | *Noted COSTELLO John Leonard R NR |
| Place of death or wounding | Armentieres, France |
| Age at death | 21.6 |
| Age at death from cemetery records | 22 |
| Place of burial | Cite Bonjean Military Cemetery (Plot IV, Row C, Grave No. 30), Armentieres, France |
| Panel number, Roll of Honour, Australian War Memorial | 131 |
| Miscellaneous information from cemetery records | Parents: John and Margaret COSTELLO, Gerangemete, Victoria. Native of Victoria |
| Other details |
War service: Western Front Medals: British War Medal, Victory Medal |