He played a key part in organizing a citizens group concerned about the location of the railway station that was built in Calgary.

[4] Reilly ran for mayor in Calgary's second municipal election in January 1886, and lost the popular vote to incumbent George Murdoch.

Stipendiary magistrate Jeremiah Travis overturned the result of the January 1886 election on weak charges of corruption by Murdoch, and appointed Reilly the mayor of Calgary.

James Reilly would contest the 1891 Canadian federal election for the Alberta (Provisional District), losing by a considerable margin to Donald Watson Davis.

In an advertisement in the February 28, 1891 Edmonton Bulletin, Reilly would explain his platform which was primarily focused on having Alberta become a province in Confederation.

While it is noted by historians that Reilly was a member of the Liberal Party of Canada, and he was supported in his election by future Liberal Member of Parliament Frank Oliver, Reilly noted in an advertisement in the Edmonton Bulletin that he is "a Conservative and supporter of that policy of Sir John A. Macdonald that has built up the financial credit of Canada...".