He was married and had two children, one of whom survived him, his only son Ulysses S. Grant V.
Chapman Grant was born in Salem Center, New York, the son of Jesse Root Grant, the youngest son of the 18th President of the United States Ulysses S. Grant. In 1892 he moved to San Diego with his parents. As a child, he spent time at the California Academy of Sciences, where he developed his interest in science. He graduated from Williams College in 1910. He became the assistant curator of entomology at the Children's Museum of the Brooklyn Institute of Arts and Sciences in September 1913. In November 1913, he left the museum for a military career beginning on the Mexican border. He was commissioned a 2nd Lieutenant in the 14th U.S. Cavalry. He married Mabel Lillian Pennebacker in December 1913. He continued his scientific studies while in the Army. When he was assigned as commandant of the Reserve Officers' Training Corps at the University of Wichita in the 1930s, he wrote scientific papers on herpetology and was curator at the Arkansas Valley Museum and Historical Society. He retired with a rank of major.
In the 1930s and 1950s several expeditions for the San Diego Museum of Natural History and the University of Illinois Museum of Natural History led him to the study of the Caribbean herpetofauna where he discovered and described fifteen new species, including the blue iguana, the cotton ginner gecko, Gaige's dwarf gecko, Klauber's dwarf gecko, Nichols' dwarf gecko, Roosevelt's dwarf gecko, Townsend's dwarf gecko, Cook's anole, the Culebra Island giant anole, Cochran's croaking gecko, the web-footed coqui, Cook's robber frog, and the whistling coqui.
In 1932 he established the scientific publication Herpetologica, the quarterly journal of the Herpetologists' League, an association of several notable herpetologists in the USA, which he co-founded in 1936. He was also the publisher of a second magazine - Scientists Forum.
In 1982 the Major Chapman Grant Hall of Ecology in the Museum of Natural History in San Diego was named in honor of him. In 1983 he died at the age of 95 in a nursing home at Escondido, California. He left one son, Ulysses S. Grant V (September 21, 1920 - March 7, 2011).
- 1935. Secondary sexual differences and notes on the mud turtle Kinosternon subrubrum in northern Indiana. American Midland Naturalist 16 (5): 798–800.
- 1935. Natrix sipedon sipedon in central Indiana, its individual and sexual variation. American Midland Naturalist 16 (6): 921–931.
- 1937. Herpetological notes from central Kansas. American Midland Naturalist 18 (3): 370–372.
- 1940. (with W. Gardner Lynn). The Herpetology of Jamaica. Bull. Inst. Jamaica Sci., Series 1: 1-148.
- 1960. Differentiation of the two southwestern tortoises (genus Gopherus), with notes on their habits. Trans. San Diego Nat. Hist. Soc. 12 (27): 441–448.
- "Chapman Grant Dead at 95; Grandson of Ulysses S. Grant". New York Times. January 15, 1983.
- "Ulysses S Grant V Dies at 90". New York Times. 2011-03-08.
- Hollingsworth, Heather (2011-04-09). "Ulysses S. Grant V, 1920-2011, Last Surviving Great-Grandson of President". Chicago Sun-Times.
- Obituary, Los Angeles Times, January 17, 1983, p. C4.
Web site of the Herpetologists' League. www.herpetologistsleague.org/en/index.php.