Son of Michael and Mary O’Neill, of Greystones, County Wicklow, Eire.
- Surname: O'Neill
- Forename: Leo Michael
- Date of birth: Not known
- Birth place: Salford, Lancashire
- Place of residence: London, Middlesex
- Gender: Male
- Age of death: 33
- Place of death: Not known
- Date of death: July 27th, 1944
- Casualty type: Not known
- Service medals: Not known
- Silver War badge: Not known
- Awards: Not known
- CWGC Memorial: Croydon (Mitcham Road) Cemetery, Surrey, UK
- CWGC reference: Plot P.P. Grave 40034.