Mark O'Brien may refer to:
Mark O'Brien (actor) (born 1984), Canadian actor Mark O'Brien (cyclist) (born 1987), Australian cyclist Mark O'Brien (footballer, born 1984), Irish footballer, plays for Shelbourne F.C. Mark O'Brien (footballer, born 1992), Irish footballer Mark O'Brien (poet) (1949–1999), American poet and disability rights advocate Mark O'Brien (hurler), Irish hurler Mark O'Brien (politician), member of the Kentucky House of Representatives