| Jack O'Brien | |
| Fullname: | Nathaniel O'Brien |
| Birth Date: | 9 June 1906 |
| Birth Place: | Yarrawonga, Victoria |
| Death Place: | Kew, Victoria |
| Height: | 185 cm |
| Weight: | 83 kg |
| Statsend: | 1931 |
| Years1: | 1928–30 |
| Games Goals1: | 13 (4) |
| Years2: | 1931 |
| Games Goals2: | 1 (0) |
| Games Goalstotal: | 14 (4) |
Nathaniel "Jack" O'Brien (9 June 1906 – 21 February 1970) was an Australian rules footballer who played with South Melbourne and Hawthorn in the Victorian Football League (VFL).[1]