Thomas Duff was an Irish architect.
Thomas Duff may also refer to:
- Thomas Duff (businessman), American businessman
- Thomas Duff (politician) (1870–1949), Australian politician
- Thomas J. Duff, American architect
- Thomas Neil Duff (1896–1978), politician in Ontario, Canada
- Tom Duff (born 1952), Canadian computer programmer
- Tommy Duff (1905–1951), English footballer