[2] A merchant and harbour commissioner,[1] French stood unsuccessfully as an anti-Treaty Sinn Féin candidate for Dáil Éireann at a by-election in 1924 for the Cork Borough constituency.

When Sinn Féin split in 1926 over the policy of abstentionism, he joined the breakaway Fianna Fáil party, and won the seat at the June 1927 general election — although like other Fianna Fáil TDs, he did not take his seat until 12 August 1927.

French was a close personal friend of Lord Mayor Tomás Mac Curtain, who was assassinated in his home by the RIC during the Irish War of Independence and of Lord Mayor Terence MacSwiney, who succeeded him in the office and also following his arrest by the same forces, died on hunger strike in Brixton Prison in 1920.

French also frequently clashed with the City Manager, Philip Monahan, during his terms as Lord Mayor.

His son, also called Seán followed him into politics and served as both Lord Mayor and TD in Cork.