Margaret Mazzantini (Italian pronunciation: [ˈmarɡaret mattsanˈtiːni]; born 27 October 1961) is an Italian-Irish writer and actress. She became a film, television and stage actor, but is best known as a writer. Mazzantini began her acting career in 1980 starring in the cult horror classic Antropophagus, she has also appeared in television and theatre. As a successful writer, her novels include Non ti muovere (Don't Move) which was adapted into the namesake film and is directed by her husband Sergio Castellitto and stars Penélope Cruz. Her career as a writer and actress has earned her several awards and nominations including Campiello Awards, a Golden Ticket Award, and a Goya Award.

Mazzantini was born in Dublin, Ireland to Carlo Mazzantini, an Italian writer and artist, and Anne Donnelly, an Irish artist. She has three sisters (one of whom is Giselda Volodi). She spent her childhood around Europe, Spain, and Tangier, until the family settled in Tivoli. In 1982 she graduated from the Academy of Dramatic Arts in Rome.

She married Sergio Castellitto in 1987. They have four children, Pietro (b. 1992), Maria (b. 1997), Anna (b. 2001) and Cesare (b. 2006). She lives in Rome.

In 2003, she was awarded the title of Knight Order of Merit of the Italian Republic on the initiative of the President of the Republic.