Moynahan is a family name with Irish origin and may refer to:
- People
- Bernard Thomas Moynahan Jr. (1918–1999), an American federal judge
- Brian Moynahan, an English writer
- Bridget Moynahan, an American model and actress
- Julian Moynahan (1925-2014), an American literary critic and novelist
- Mike Moynahan (1856–1899), an American baseball player
- Science
- 13620 Moynahan, an asteroid
- Moynahan syndrome, a skin condition