Guillaume Emmanuel Marie de Quengo de Tonquédec (born 18 October 1966) is a French stage, television and film actor. He first earned fame in his homeland for his role as Renaud Lepic in the TV series Fais pas ci, fais pas ça (2007–2017) on France 2, before winning the César Award for Best Supporting Actor for his performance in What's in a Name? in 2013. De Tonquédec was made a Knight in the Ordre des Arts et des Lettres in 2015 by Minister of Culture Fleur Pellerin. A native of Paris, Guillaume de Tonquédec grew up in Louveciennes. He studied economics and English at Paris Nanterre University until he joined the Conservatoire national supérieur d'art dramatique in Paris in 1986 for a three-year programme. In 1989, he began his stage career with a national tour in John Millington Synge's The Playboy of the Western World.

He gained recognition in film in Krzysztof Kieslowski's The Double Life of Veronique (1991), followed by his role as Claude Jade's son Jules Martin in List of Merite (1992). In 1996, he starred in Raúl Ruiz's Three Lives and Only One Death.