MacFadyen is a Scottish patronymic surname meaning "son of little Patrick". The Celtic prefix "Mac" means "son of", while "Fadyen" is a derivative of the Gaelic Pháidín, meaning "little Patrick". It is a variant of the surname McFadden, which has other variants. People with the surname include:
Allan Macfadyen (1860–1907), Scottish bacteriologistAngus Macfadyen (born 1963), Scottish actorChristie MacFadyen, Canadian actressDonnie Macfadyen (born 1979), Scottish rugby playerDonald Macfadyen, Lord Macfadyen (1945–2008), Scottish lawyer and judgeElmer MacFadyen (1943–2007), Canadian politicianIan Macfadyen, (born 1942), British retired Air MarshalMatthew Macfadyen (born 1974), English actorRoss Macfadyen, Scottish broadcast professionalWillie MacFadyen (1904–1971), Scottish football player and manager