John Ferdinand Smyth Stuart (1745 – 20 December 1814), known until 1793 as John Ferdinand Smyth and mostly after that as Ferdinand Smyth Stuart, was a Scottish-born American loyalist and physician who claimed to be a great-grandson of King Charles II. As the author of A Tour in the United States of America (1784), he used the name John Ferdinand Dalziel Smyth.
Leaving America during the Revolutionary War, Stuart spent the rest of his life in England and the West Indies.