In 1873, he joined the River Thames Barge Builders Trades Union, becoming its general secretary in 1879 and holding the post until 1908.

In 1892, Steadman was elected as a Progressive Party member of London County Council (LCC), representing Stepney.

[citation needed] Steadman was finally elected as a Lib–Lab Member of Parliament (MP) for Stepney at the March by-election in 1898 which took place because of the death of F. W. Isaacson in February, who had held the seat since 1896.

In 1899, he was elected to the Parliamentary Committee (later the General Council) of the Trades Union Congress (TUC), and in 1902 he was its President.

He went on to chair the first conference of the Labour Representation Committee, but left the organisation when asked to leave the Liberal Party.