Michael or Mike Brennan may refer to:
- Michael Brennan (actor) (1912–1982), English film and television actor
- Michael Brennan (footballer) (born 1965), former Australian rules footballer
- Michael Brennan (field hockey) (born 1975), Australian field hockey player
- Michael Brennan (finance) (born 1942), American finance professor
- Michael Brennan (Fine Gael politician) (1884–1970), Irish Cumann na nGaedhael and (later) Fine Gael TD
- Michael Brennan (ice hockey) (born 1986), American professional ice hockey player
- Michael Brennan (Lieutenant-General) (1896–1986), Irish Defence Forces Chief of Staff 1931–1940
- Michael Brennan (photographer) (born 1943), British photographer
- Michael Brennan (Progressive Democrats politician) (born 1946), Irish Progressive Democrat Senator
- Michael Brennan (poet) (born 1973), Australian poet
- Michael Brennan Jr., record producer of songs as "Ask Me How I Am" and "One Night Is Not Enough"
- Michael B. Brennan (born 1963), American lawyer and United States federal judge
- Michael F. Brennan (born 1953), mayor of Portland and Maine state senator
- Mike Brennan (basketball) (born 1972), American college basketball head coach
- Mike Brennan (American football) (born 1967), American football tackle