After the military registration carried out in early 1867, 600 black people and 307 white people were on the voter rolls in McIntosh. In late 1867, Campbell was elected as one of two delegates from the second senatorial district – Liberty, McIntosh, and Tattnall counties – to Georgia's constitutional convention. In April 1868, Campbell was elected as the state senator for the second district, and his son Tunis G. Campbell Jr. was elected as state representative for McIntosh County. While both Campbells were among the black legislators expelled later in 1868, they were able to return to office in 1871; Campbell Sr. left office in 1872, while Campbell Jr. served until 1874.