Daniel, Danny or Dan O'Sullivan may refer to:
Daniel O'Sullivan (musician) (born 1980), English musician Daniel O'Sullivan (priest) (1846–1928), Irish priest and theologian Danny O'Sullivan (Australian rules footballer) (born 1952) Danny O'Sullivan (boxer) (1923–1990), English boxer Dan O'Sullivan (basketball) (born 1968), American basketball player Dan O'Sullivan (Gaelic footballer) (1927–2013), Irish Gaelic footballer Dan O'Sullivan (historian), British author of Wikipedia – A New Community of Practice?