Daniel O'Brien
Daniel or Dan O'Brien may refer to:
Politicians and nobles
- Daniel O'Brien, 1st Viscount Clare, MP for County Clare, younger son of Connor O'Brien, 3rd Earl of Thomond
- Daniel O'Brien, 3rd Viscount Clare, son of Connor O'Brien, 2nd Viscount Clare
- Daniel O'Brien, 4th Viscount Clare, son of Daniel O'Brien, 3rd Viscount Clare
- Daniel O'Brien (Jacobite), Irish Jacobite soldier and diplomat
- Daniel Pitt O'Brien, Secretary of State of West Virginia
Sportspeople
Athletes
- Dan O'Brien, American decathlete
- Dan O'Brien (footballer), Australian rules football player
- Dan O'Brien (pitcher), American baseball player
- Dan O'Brien (soccer), American soccer player
- Danny O'Brien (gridiron football), American college football quarterback
Coaches / executives
- Dan O'Brien (American football), American college football coach and administrator
- Dan O'Brien (baseball coach), American college baseball coach
- Dan O'Brien Sr., American baseball executive, general manager of Rangers, Mariners, Angels
- Dan O'Brien (baseball executive), American former baseball executive, general manager of Reds; son of Dan O'Brien Sr.
Writers / journalists
- Daniel O'Brien (comedian), American humorist, writer and comedian
- Dan O'Brien (author), American author and rancher
- Dan O'Brien (playwright), American playwright
- Dan O'Brien (sports journalist), American sports journalist, author and screenwriter
- Danny O'Brien (journalist), British technology journalist