Architecture writer Christopher Gray called him "one of the most prolific architects of the period" (the mid-19th century). The American Institute of Architects in 1908 called him "the most fashionable architect of his generation." Many of his notable buildings are found in New York City.
- St. Nicholas Hotel (1853), 507-27 Broadway, demolished. 1,000 guest rooms.
- Fifth Avenue Hotel (1859), 200 Fifth Avenue (23rd to 24th Streets), demolished. Replaced by Robert Maynicke's Toy Center Building, 1909.
- Astor Library (1859 expansion), 444 Lafayette Street. Now the center section of The Public Theater.
- Mortimer Building (1862), 935 Broadway (159 Fifth Avenue). Now Restoration Hardware Building.
- National Park Bank Building (1868, altered 1905), 214-18 Broadway, demolished 1961
- Pike's Opera House (1868), 8th Avenue & 23rd Street, later renamed the Grand Opera House, demolished 1960.
- Arnold Constable Building (1869), Broadway & West 19th Street
- New York Life Insurance Building (1870), 346 Broadway. Altered and expanded by McKim, Mead & White, 1904.
- Gunther Building (1872), 469-75 Broome Street, cast-iron facade.
- "Correspondence: The Death of Mr. Griffith Thomas", The American Architect and Building News Vol. 5 No. 161, January 25, 1879, pp. 29–30. Online at Google Books.
- "On Canal Street, a Sooty Survivor of a Grander Time", by Christopher Gray, New York Times, March 26, 2006.
- Architectural Record No. 24, American Institute of Architects, p. 303.
- Brooklyn's Green-Wood Cemetery: New York's Buried Treasure, by Jeffrey I. Richman
- "A New Metropolitan Theater—Pike's Opera House", New-York Tribune, July 1, 1867, p. 4, col. 6
- New York: A Guide to the Metropolis, by Gerard R. Wolfe
- "The Gunther Building", New York Architectural Images.
- "Arnold Constable Building", by edenpictures, on Flickr.
- "The Old Astor Library, Now the Joseph Papp Public Theater", by Christopher Gray, New York Times, February 10, 2002.
- "Former New York Life Insurance Company Building", The Masterpiece Next Door, archived by Internet Archive's Wayback Machine on December 7, 2008.
- Green-Wood Cemetery Burial Search