Patrick O'Brien may refer to:
- Patrick O'Brien (artist) (born 1960), illustrator and author of children's books
- Patrick O'Brien (Australian politician) (1810–1882), politician in Victoria, Australia
- Patrick O'Brien (footballer, born 1875) (1875–1951), Scottish footballer
- Patrick O'Brien (footballer, born 1884) (1884–?), Scottish footballer and surgeon
- Patrick O'Brien (musician) (1947–2014), American musician and lutenist
- Patrick O'Brien (political scientist) (1937–1998), politics professor, University of Western Australia
- Patrick Cotter O'Brien (1760–1806), the tallest person alive in his lifetime
- Patrick Joseph O'Brien (1835–1911), Member of Parliament for North Tipperary, 1885–1906
- Patrick K. O'Brien (born 1932), British academic and historian
- Patrick Thomas O'Brien (born 1951), American actor
- Sir Patrick O'Brien, 2nd Baronet (1823–1895), Irish politician
- Pat O'Brien (Irish politician) (Patrick O'Brien, c. 1847–1917), Irish Nationalist MP in the United Kingdom Parliament