His contemporaries respected his organizational skills and perceived him as a potential Conservative leader after Prime Minister Sir John A. Macdonald vacated the leadership.

[3] However, he broke with the Conservatives in the 1890s, running and being re-elected as an Independent Member of Parliament (MP) in the 1891 Canadian federal election.

He appears to have been associated with the Equal Rights Party which ran in that election but did not run as their candidate.

He appeared in the Supreme Court of Canada in the significant constitutional case of Citizens Insurance Co of Canada v Parsons, arguing successfully on behalf of two individuals claiming compensation under fire insurance policies.

Following the 1896 election, McCarthy forged an alliance with the Liberal Party, even though its leader Wilfrid Laurier was a French Canadian Catholic.