Tim O'Brien may refer to:
- Tim O'Brien (author) (born 1946), American author
- Timothy O'Brien (endocrinologist), Irish professor
- Timothy L. O'Brien (born 1961), American journalist
- Tim O'Brien (producer), music producer, particularly associated with producing The Chambers Brothers.
- Tim O'Brien (musician) (born 1954), American musician
- Sir Tim O'Brien, 3rd Baronet (1861–1948), Irish-born cricketer
- Tim O'Brien (politician) (born 1968), legislator in the Connecticut House of Representatives
- Father Timothy O'Brien, a Catholic priest involved in a U.S. Congressional Chaplain controversy
- Tim O'Brien (illustrator) (born 1964), American artist
- Timothy O'Brien (theatre designer) (born 1929), British theatre designer