 In 1861 President Abraham Lincoln appointed Leavenworth the United States' commissioner for the convention with Granadine Confederation in 1861 and 1862.Leavenworth was elected as a Republican to the Forty-fourth United States Congress, holding office from March 4, 1875 to March 3, 1877.He declined to be a candidate for renomination in 1876 and resumed business activities in Syracuse.