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 studied medicine with James Mitchell in Dundas, attended the University of Toronto and received a medical degree from Victoria College.
He returned to Dundas in 1852 and joined the practice of Doctor Mitchell.
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.