During Burwell’s management of Carter’s Grove the plantation prospered, and he also moved some of his slaves to his Frederick County property and improved production there during the 1770s and 1780s. As the proprietor of a major plantation and a member of a leading family he succeeded to the offices appropriate to his station. Burwell was appointed to the James City County Court on November 6, 1772, was a colonel in the militia by 1774, and served on the James City County Committee that same year. On November 27, 1776, he became county lieutenant, the commander of the county’s militia. Burwell represented James City County in the House of Delegates in 1778 and 1779 and served on the Committee of Propositions and Grievances during both years and on the Committee of Religion in 1779. He was elected again in 1782 and served on the Committee of Propositions and Grievances during the short session in May but missed the poorly attended October session. Burwell was also one of the directors of the Public Hospital in Williamsburg.
In 1788 Burwell was one of two men elected to represent James City County in a convention called to consider the proposed constitution of the United States. He did not take an active part in the debates, but his opinions were well known. Burwell voted against insisting on amendments prior to ratification and against reducing the taxing power of Congress, and on June 25, 1788, he voted to ratify the Constitution.
Burwell’s wife died scarcely a month after the convention adjourned, and on January 24, 1789, he married Lucy Page Baylor, widow of George Baylor (1752–1784). They had five sons and three daughters. Burwell transferred his seat from James City County to Frederick County not long after his second marriage. By 1790 he owned approximately 8,000 acres of land in the lower Shenandoah Valley. Burwell lived in the portion of Frederick County that in 1836, after his death, became Clarke County. During the 1790s he constructed Carter Hall, one of the largest and most elegant stone mansions in that part of Virginia. Burwell named it in honor of his great-grandfather,(d. 1732), from whom the family had inherited the land. Burwell established a ferry on the Shenandoah River, erected two gristmills, two distilleries, a cooper’s shop, an iron forge, a sawmill, and a tannery, and built a school for his children and other local students. Burwell also had a passion for breeding fine horses.
Nathaniel Burwell died at Carter Hall on March 29, 1814, and was buried nearby in the Old Chapel cemetery.