With his fame earned from this case, in 1910, Lafferty was elected as a Republican to the United States House of Representatives, representing Oregon's 2nd congressional district. In 1912, after Oregon was granted another congressional district based on the 1910 census, he was elected to represent Oregon's 3rd congressional district, running as both a Republican and a Progressive, allying himself with Progressive Presidential candidate Theodore Roosevelt. Lafferty identified himself as a Progressive Republican for the 63rd United States Congress. While in Congress, Lafferty continued his fight on behalf of his constituents affected by the railroad land issue. He also supported equal suffrage for men and women.