| James McMahon | |
| Office1: | Ontario MPP |
| Term Start1: | 1875 |
| Term End1: | 1894 |
| Predecessor1: | Thomas Stock |
| Successor1: | John Ira Flatt |
| Constituency1: | Wentworth North |
| Party: | Liberal |
| Birth Date: | 1 July 1830 |
| Birth Place: | Dundas, Upper Canada |
| Death Place: | Toronto, Ontario |
| Occupation: | Doctor |
| Spouse: | Julia Ball (m. 1858) |
James McMahon (July 1, 1830 - 1909) was an Ontario doctor and political figure. He represented Wentworth North in the Legislative Assembly of Ontario as a Liberal member from 1875 to 1894.
He was born in Dundas, Upper Canada in 1830, the son of Irish immigrants who came to Upper Canada in 1819. He studied medicine with James Mitchell in Dundas, attended the University of Toronto and received a medical degree from Victoria College. He was licensed as a doctor and then set up practice in Ayr in 1850. He returned to Dundas in 1852 and joined the practice of Doctor Mitchell. After Mitchell died of cholera in 1854, McMahon took over his practice. He married Julia Ball in 1858. McMahon served on the town council for Dundas and was mayor in 1866. After the sitting member Thomas Stock was disqualified, he was elected in an 1875 by-election to represent Wentworth North in the Ontario legislative assembly.