Edward Seymour Hammatt was born in Geneseo, New York. His family moved to Rochester, New York where he was educated. He graduated from Lehigh University and the Massachusetts Institute of Technology, and then spent four years working for Ware & Van Brunt in Boston. He spent a further four years with the New York firm of Hardenbergh & Le Brun. He was also associated with John B. Snook. Hammett opened his own office in Davenport, Iowa in 1883 where he worked until a few months before his death. His notable buildings include schools, business and residential buildings and churches for the Episcopal Diocese of Iowa. In 1884 he was elected to membership in the Western Association of Architects. He became a Fellow of the American Institute of Architects in 1889 after the groups consolidated.
The following buildings are listed on the National Register of Historic Places:
- Kemper Hall, a contributing property in the College Square Historic District, Davenport, Iowa (1885)
- One or more buildings in the St. Katherine's Historic District, Davenport, Iowa (1885, 1886)
- Connor House, Rock Island, Illinois (1888)
- Edward Edinger House, Davenport, Iowa (1890)
- Lincoln School, Rock Island, Illinois (1893)
- Trinity Episcopal Church, Ottumwa, Iowa, a contributing property in the Fifth Street Bluff Historic District (1895)
- Trinity Memorial Episcopal Church, Mapleton, Iowa (1896)
- "Edward Seymour Hammett". archinform. Retrieved 2012-05-01.
- "Obituary". American Institute of Architects. Retrieved 2012-05-01.
- Svendsen, Marls A., Bowers, Martha H (1982). Davenport—Where the Mississippi Runs West: A Survey of Davenport History & Architecture. Davenport, Iowa: City of Davenport. p. 13-2.
- "Fifth Street Bluff Historic District". Wapello County. Retrieved 2012-05-01.