Warner Washington III (December 7, 1771 - September 11, 1793) was a cousin of the first President of the United States, George Washington, and a doctor of medicine in Philadelphia, Pennsylvania.

Washington was born at the "Clifton" estate in Clark County, Virginia on December 7, 1771 as the son of Warner Washington, Jr. and Mary Whiting. He grew up in the area and studied medicine under the tutelage of Dr. Benjamin Rush in Philadelphia, Pennsylvania. He wrote multiple letters to George Washington in 1793 during his presidency. During his time in Philadelphia, he contracted a number of debts and wrote to Washington under the idea that he knew his grandfather, Warner Washington. Unfortunately, Washington believed that his debts were the result of extravagance and wrote instead to his father about conveying money.

Washington died there in Philadelphia only months later, on September 11, 1793, from a yellow fever epidemic. He was unmarried and had no children. His two letters to George Washington, however, in that summer of 1793 were preserved in the Mount Vernon archives.

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