Weakley joined the Revolutionary Army at the age of sixteen and served until the close of the American Revolutionary War, fighting in the battles of Alamance and Guilford Courthouse. On April 18, 1782, Weakley left his home in Halifax County with a horse, bridle and saddle, and $1.75. He went to Rowan County, North Carolina to study surveying with General Griffith Rutherford. During the winter of 1783, he moved to the Cumberland settlements, and set up residence on Whites Creek in Davidson County. He moved to his estate in Nashville, "Lockeland", in 1800. Weakley was also a co-founder of the town of Jefferson in Rutherford County, Tennessee. He and Thomas Bedford, a fellow land speculator, were granted as assignees a North Carolinaland grant and had laid out 102 town lots and a Public Square by 1803, at the junction of the East and West Forks of the Stones River. The town of Jefferson was the first county seat of government for Rutherford County, and contributed immensely to the early economic development of the area during the first decade after its formation. The Stones River provided for direct access for goods and commodities such as timber and other cash crops to be shipped by flat boat to the Cumberland River and Nashville and thereby to far away ports such as New Orleans, Pittsburg, and beyond. In 1819, Weakley, along with several other notable early Nashville residents such as Dr. John Shelby, petitioned the Tennessee Assembly for permission to establish the Nashville Bridge Company. Weakley and Shelby subsequently served as commissioners for the newly formed company. By 1823, the Nashville Bridge Company's first bridge project, which was also the first covered bridge to span the Cumberland River, was completed near the Public Square in Nashville at a cost of $75,000. This bridge was demolished in 1851 to allow for larger and taller steamboats to access the commercial wharfs at Nashville. In 1785, Weakley moved to the part of North Carolina that later became Tennessee and engaged in agricultural pursuits. He was a member of the North Carolina convention that ratified the Constitution of the United States in 1789. In 1791, he was the Brigade Inspector of the militia of Mero District, in what was then the Southwest Territory. In 1796 he was elected to the first Tennessee House of Representatives. In 1798, he was a Colonel of the 2nd Regiment of the Davidson County Militia. He served as Senator in the Tennessee Senate in 1799, 1803, 1807 and 1819. Weakley was elected as a Democratic-Republican to the Eleventh Congress, which lasted from March 4, 1809 to March 3, 1811. In 1819, Weakley was appointed commissioner to treat with the Chickasaw Indians. He served as Speaker of the Tennessee Senate from 1819 to 1821 and from 1823 to 1825. He was a member of the state constitutional convention in 1834.
