Thomas Johnston was born in about 1720 and was a resident of Onslow County, North Carolina. A local justice of the peace, in 1769 Johnston heard a legal case involving Cuff, an enslaved man charged with a crime. During the American Revolution he served as a major in the Onslow County Regiment of the North Carolina Militia. He also represented Onslow in the North Carolina House of Representatives in 1782 and as a state senator in 1784 and 1788. Johnston died in Newberry County, South Carolina in about 1796.