 At the 1865 general election he was elected as the Member of Parliament (MP) for Great Grimsby, defeating the sitting Conservative MP John Chapman, who was also a director of the Manchester, Sheffield and Lincolnshire Railway.Both candidates had canvassed vigorously during the campaign, with Fildes describing himself as a Liberal who had "ever supported measures conducive to the elevation and improvement of the condition of the people".At the 1868 general election, there was no Conservative candidate in Grismby.