John Barrett (November 28, 1866 – October 17, 1938) was a United States diplomat and one of the most influential early directors general of the Pan American Union.

On his death, the New York Times commented that he had "done more than any other person of his generation to promote closer relations among the American republics".

While working as a journalist, he so impressed President Grover Cleveland during a meeting that he was appointed as the United States U.S. Minister to Siam (now Thailand).

In 1903, he was appointed as the Minister to Argentina, and though he only served in that position for one year, President Theodore Roosevelt later remarked that he had begun a "new United States-Argentine era".

In 1924, he briefly entered politics by running for the United States Senate as a Republican, but withdrew from the race before the election.