William Loughton Smith (1758 – December 19, 1812) was an American lawyer, politician, and diplomat from Charleston, South Carolina.

[3] His father earned his fortune as an importer of British luxury goods (primarily furniture and high-end silverware) into Charleston.

[5] Smith was known for being outspokenly pro-George Washington and was elected as a Pro-Administration candidate to the First Congress in 1788 to South Carolina's 1st congressional district.

This was the first invocation of Congress's power, established under Article I, Section 5 of the Constitution, to serve as the "Judge of the Elections, Returns and Qualifications of its own Members"; the House found that Smith was qualified, with James Madison noting that "it is an established maxim, that birth is the criterion of allegiance.

[5] As chair of the Committee on Ways and Means, Smith acted as a Federalist floor leader and was known as a close collaborator and House spokesman for Treasury Secretary Alexander Hamilton.

Smith returned to Charleston and ran for Congress again in 1804, 1806, and 1808, but lost all of those elections to the Democratic-Republican Party candidate Robert Marion.

In 1808, his politics shifted away from Alexander Hamilton and toward Thomas Jefferson, with Smith embracing the Embargo Act of 1807 as a way to increase the U.S.'s self-sufficiency.