Grennan is an Irish surname. It may be of Norman origin, from the French name Grenan. Notable people with the surname include:
Eamon Grennan (born 1941), Irish poet James Grennan, Irish Gaelic footballer who played for Offaly Justin Grennan (born 1978), American singer Keith Grennan (born 1984), American football player Mike Grennan (1950–2009), American curler Seán Grennan, Irish dual player of Gaelic football and hurling who played for Offaly Tom Grennan (born 1995), English singer and songwriter Winston Grennan (1944–2000), Jamaican drummer Jacqueline Grennan Wexler (1926–2012), American academic administrator
See also Greenan (surname) Julia Grenan (1884–1972), Irish nationalist and socialist in the Easter Rising Grennan (disambiguation)