1750–1 Mar. 1818
Irwin held a number of local offices including inferior court justice, justice of the peace, and road commissioner; after moving to Washington, he served with commissioners in negotiating treaties with the Indians. As early as 1783, he participated in the first of a number of conventions and legislatures in the formation and inauguration of the state government. He also served in the convention that ratified the federal Constitution. He was a member of the state legislature from 1790 to 1811, except during the years when he was governor of Georgia (1796–98 and 1806–8). During his first term as governor, he took satisfaction in signing a bill to rescind the Yazoo land act by which a previous legislature, through bribery, had sold thirty-five million acres of western land to four land companies for 1.5 cents an acre.
Although the records are not clear, it appears that Irwin was married twice. His first wife's maiden name was Steward; his second wife's given name was Isabella, whom he probably married after 1772. His children were Rebecca, Mary Elizabeth, Nancy, Thomas, John, Jared, Jr., Jane, Isabella, and Ann. In addition, he adopted a nephew, Jared, Jr., the son of his brother Alexander. Two of his sons, Jared, Jr., and Thomas, were among the earliest graduates of the University of Georgia after it opened in 1801. Irwin died at his home, Union Hill, where he was buried near Ohoopee Baptist Church.