 He was elected to two four-year terms (beginning in 1883 and 1887), but left the Senate in 1889 following his election to Congress.In 1888, Sweney was elected as a Republican to the Fifty-first Congress, following the decision of incumbent Republican William E. Fuller not to seek a third term.However, his re-election bid was thwarted when he was upset by Democrat Walter Halben Butler as part of a Democratic landslide in 1890.