John Hennessy Saul (December 25, 1819 – May 11, 1897) was an Irish-born American horticulturist and landscape architect who assisted in the planning and the development of the National Mall in Washington, D.C., and served as the first chairman of Washington, D.C.’s parks commission.

[1][3][4] From 1851 to 1853, he was responsible along with William Dunlop Brackenridge for improving the National Mall, Lafayette Square, and the Smithsonian Museum grounds.

He operated twenty greenhouses using his horticultural skills to create numerous new varieties of plants.

He was a member of the American Society of Florists and was a frequent contributor to the journal The Horticulturalist.

Saul died on May 11, 1897, at his home on Brightwood Road (now Georgia Avenue) in Washington, D.C.[1][7] He was interred at Mount Olivet Cemetery.