Daniel O'Leary
Daniel O'Leary may refer to:
- Daniel O'Leary (chemist), American chemist
- Daniel O'Leary (mobster) "Danny", Philadelphia mobster
- Daniel O'Leary (Irish nationalist politician), Irish Parliamentary Party MP for West Cork
- Daniel Florence O'Leary, Irish-born South American brigadier general
- Daniel O'Leary (Fine Gael politician), Irish Cumann na nGaedhael / Fine Gael politician from Cork
- Dan O'Leary (American football), American football player
- Dan O'Leary, baseball player
- K. Daniel O'Leary, American psychologist