John Preston Buchanan (January 30, 1888 – September 15, 1937) was an American politician who served as a member of the Virginia Senate, representing the state's 1st district.

Buchanan was born in the town of Marion in Smyth County, Virginia on January 30, 1888.

After high school, Buchanan attended Washington and Lee University.

A Democrat, Buchanan defeated Republican Robert A. Anderson in 1915 to serve as a senator during the 1916 General Assembly; the seat was occupied by his father in the previous session.

Buchanan married Annabel Morris on August 14, 1912 in Salem, Virginia.