Robertson returned to North Carolina and married Charlotte Reeves in 1767. They started farming. In 1769, Robertson accompanied explorer Daniel Boone on his third expedition to lands beyond the Allegheny Mountains. The party discovered the "Old Fields" along the Watauga River valley, where Elizabethton, Tennessee later developed. Robertson stopped here to plant corn while Boone continued on to Kentucky. After returning to North Carolina, Robertson became involved with the Regulator movement. They recruited a group of settlers to return to the Watauga River valley, which they believed to be in Virginia. In 1772, Robertson and the pioneers who had settled in Northeast Tennessee met at Sycamore Shoals to establish an independent regional government known as the Watauga Association. However, in 1772, surveyors placed the land officially within the domain of the Cherokee tribe, who had long occupied this area. They required the settlers to negotiate a lease to cultivate and settle on their land. As the signed lease was being celebrated, a Cherokee warrior was murdered by a white man. Robertson's skillful diplomacy made peace with the irate Cherokee, who threatened to expel the settlers by force if necessary. In 1775, a treaty meeting was held between the Cherokee and a delegation of the Transylvania Company, headed by Richard Henderson. Under the Treaty of Sycamore Shoals, the Transylvania Company purchased a vast amount of land from the Cherokee, including most of present-day Kentucky and part of Tennessee. The treaty was technically illegal since only the government could have formal transactions and purchase land from Native American tribes.. During the treaty process, Dragging Canoe, son of Cherokee chief Attacullaculla, made a speech condemning the sale of any Cherokee land, which the tribe held in common for the use of all. He broke from the general Cherokee tribal government to form a band that the pioneers called the Chickamauga Cherokee or Chickamauga, for their settlement, although the people never had a separate tribal identity. After Henderson's Transylvania Company had bought Kentucky, Daniel Boone was hired to widen the Indian path over Cumberland Gap to facilitate migration by Anglo-American pioneers. This road became known as the Wilderness Road. Robertson's group lived at Watauga in peace until July 1776, when Chief Old Abraham of Chilhowee led a Cherokee contingent that attacked Fort Watauga. A 40-man contingent commanded by John Carter, with Robertson and John Sevier as lieutenants, withstood a siege of about two weeks. After the Cherokee were subjugated later that year, the governor of North Carolina appointed Robertson as Indian agent to reside at the Cherokee capital. He was to prevent them from forming an alliance with the British to fight as their allies against the rebels during the American Revolution.
In the spring of 1779, during the Revolutionary War, Robertson and John Donelson founded Fort Nashborough, later to become Nashville. It was then part of the Washington District, North Carolina. He represented Davidson County, in the North Carolina legislature and had the settlement established as a town. He also established the first school there, the historic Davidson Academy for male students. The Spanish governor of former French territory west of the Mississippi River offered Robertson peace and the free navigation of the Mississippi in exchange for his leaving the United States and establishing — along with the Watauga settlement and Kentucky — an independent government. He refused to consider the matter. In 1790, Robertson was appointed brigadier-general of the territorial militia by U.S. President George Washington, serving until 1796. He shared with Sevier the honor and affection of Tennesseans. He was appointed as Indian commissioner, serving until his death in 1814. Robertson died near Memphis and was buried there. His family had his remains moved and re-interred in 1825 in the Nashville City Cemetery, to memorialize his contributions there. His son, Felix Robertson, served as Mayor of Nashville from 1818 to 1819. Robertson's great-granddaughter, Medora Cheatham, married Telfair Hodgson Jr., the treasurer of and a developer of Belle Meade, Tennessee. She was the honorary president-general of the United Daughters of the Confederacy.
Legacy and honors
A memorial obelisk was installed in his honor in the Nashville City Cemetery.
