Hamilton was an uncompromising Republican, violently opposed to secession. During Reconstruction he was appointed state comptroller in 1867 and was a delegate to the Constitutional Convention of 1868-69. His participation caused some controversy at the convention, since he was part of a Radical Republican faction that called for the disfranchisement of all former Confederates. He was elected as a Republican to the United States Senate in 1870 and served until 1877. After retirement from public life he traveled extensively. During his last years he resided in Brooklyn, New York, and made occasional trips to Austin. He never married. Hamilton died on November 21, 1893, while visiting in San Diego, California. He was buried in Oakwood Cemetery, Austin, and his fortune was divided among his relatives.
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