Charles Johnston was a resident of Tyrrell and Chowan Counties. In 1777 he served as a justice of the peace or court clerk in Tyrrell County, and in that role he received sworn depositions from several people about their knowledge of the Gourd Patch Conspiracy in preparation for the trial of the plot's leading members. He later represented Chowan County in the North Carolina State Legislature for many years and voted for North Carolina to join the United States and ratify the constitution in 1789.