Chamberlain entered politics as a delegate to the 1868 South Carolina Constitutional Convention from Berkeley County. He served as state attorney general from 1868–1872 in the administration of Governor Robert K. Scott. After he failed to win the Republican nomination for governor in 1872, Chamberlain practiced law in Charleston. His partner later recalled that he worked hard for little compensation; whatever his ethics in office, he certainly had not amassed a fortune. In 1873, he was elected to the board of trustees of the University of South Carolina as the first black students were admitted and faculty hired for the institution.