| Johnnie Mercer | |
| Fullname: | John Thompson Mercer |
| Birth Date: | 27 March 1877 |
| Birth Place: | Belfast, Ireland |
| Years1: | 1893 |
| Clubs1: | Belview |
| Years2: | 1893 |
| Clubs2: | Ligoniel |
| Years3: | 1894–1895 |
| Clubs3: | 81st North Lancashire Regiment |
| Years4: | 1895–1896 |
| Clubs4: | 8th Belfast Boys Brigade |
| Years5: | 1896 |
| Clubs5: | Linfield Swifts |
| Years6: | 1896–1897 |
| Clubs6: | Preston North End |
| Caps6: | 0 |
| Goals6: | 0 |
| Years7: | 1898–1899 |
| Years8: | 1899–1900 |
| Years9: | 1900 |
| Caps9: | 9 |
| Goals9: | 2 |
| Years10: | 1900–1902 |
| Clubs10: | Linfield |
| Years11: | 1902–1903 |
| Years12: | 1903–1905 |
| Caps12: | 26 |
| Goals12: | 1 |
| Years13: | 1905–1906 |
| Years14: | 1906–1908 |
| Clubs14: | Colne |
| Years15: | 1908 |
| Totalcaps: | 35 |
| Totalgoals: | 3 |
| Nationalyears1: | 1898–1905 |
| Nationalcaps1: | 12 |
| Nationalgoals1: | 1 |
John Thompson Mercer (27 March 1877–1947) was an Irish footballer who played in the Football League for Derby County and Leicester Fosse.[1]