As colonel leading a state militia, in 1776 he prevented the British from taking Charleston, and Fort Moultrie was named in his honor.

After independence, Moultrie advanced as a politician; he was elected by the legislature twice within a decade as Governor of South Carolina (1785–1787, 1792–1794), serving two terms.

His parents were the Scottish physician Dr. John Moultrie and Lucretia Cooper, and he acquired a slave plantation, enslaving over 200 African Americans.

That spring when Maj. Gen. Benjamin Lincoln took the bulk of the American force towards Augusta, Georgia, Moultrie was stationed at Black Swamp with a small contingent to watch the British on the other side of the Savannah River.

He refused to surrender at a time when the civilian authorities in Charleston felt somewhat abandoned by the Continental Congress and were almost ready to give up.

The state constitution prohibited men from serving two successive terms as governor, an effort to keep power in the hands of the legislature.

[5] During his notable defense of the fort in 1776, a flag of Moultrie's own design was flown: a field of blue bearing a white crescent with the word LIBERTY on it.