He served as Sheriff of Bute County, but with the coming of the American Revolution, he became a strident patriot, and was elected to North Carolina's Provincial Congress.

He served with distinction in the battles of Stono Ferry and Eutaw Springs, but recurring bouts of poor health often forced him to play an administrative role, or to convalesce in North Carolina.

[8] Like many former Virginians who moved across the border into North Carolina during the colonial era, it is likely that Sumner would have retained close business ties with the province of his birth.

[1] In November 1775, Sumner summoned his militia into active service, and marched north to join Robert Howe in capturing (and later burning) Norfolk, Virginia.

[15] On April 4, 1776, after the American Revolutionary war had been raging in Massachusetts for nearly a year, the Provincial Congress at Halifax chose Sumner to be colonel, and thus commanding officer, of the 3rd North Carolina Regiment.

This dispute was resolved only when a military court of inquiry awarded Muhlenberg temporary command after Sumner failed to appear and plead his case.

He and his men drilled regularly and had their supplies and arms inspected and repaired, although many of the North Carolinians had such poor muskets that a substantial number were discarded.

Generals Alexander McDougall of New York and Lachlan McIntosh of Georgia were appointed in succession to temporary command of the North Carolinians while in winter quarters.

Many North Carolina officers believed the state was due the appointment of two additional brigadier generals based on the number of soldiers it provided to the Continental Army.

[20] At Valley Forge, the North Carolina brigade had a total strength of 1,051, but 353 were ill, and 164 lacked sufficient clothes to be fit for service.

[26] On June 20, 1779, Sumner led a Continental Army brigade at the Battle of Stono Ferry, assaulting the British right flank and routing the Hessian von Trümbach Regiment.

At least seven Continental officers under Sumner's command were wounded, and future United States President Andrew Jackson's brother Hugh was among ten North Carolinians killed.

[34] As commander of a brigade of North Carolina militia, Sumner was tasked with defending the state from the advances of British General Charles Cornwallis,[1] but the militiamen were poorly equipped and ill-trained.

[39] On September 8, his regiments were positioned on the right flank of the Continental Army at the Battle of Eutaw Springs, where his units served a vital role in halting several British assaults.

[1] Greene commented on the North Carolinians' actions at Eutaw Springs, stating that they "fought with a degree of obstinacy that would do honor to the best of veterans".

[4] Greene primarily wanted him to regain control of the military situation in the state, as then-Governor and former Continental Congress delegate Thomas Burke had been captured by David Fanning in a stunning daylight raid on Hillsborough, North Carolina on September 12, 1781.

[46] He was originally buried eight miles (13 km) outside of Warrenton,[47] but in 1891 his remains were moved to the Guilford Courthouse Battlefield, where they were interred under a monument intended as part of a "shrine to patriots".