Mark O'Brien

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 advocate for the disabled
 * Mark O'Brien (hurler), Irish hurler