Chaplin was born in Madrid to English-American actressGeraldine Chaplin and Chilean cinematographer Patricio Castilla.[2][3] She has a half-brother named Shane from her mother's previous relationship with film directorCarlos Saura.[3] Her paternal grandmother, Hilda Valderrama, was aMapuche human rights lawyer.[4] A member of theChaplin family, she is a granddaughter of English filmmaker and actorCharlie Chaplin, and great-granddaughter of Irish-American playwrightEugene O'Neill.[5] She was named after her maternal grandmotherOona O'Neill, Charlie Chaplin's fourth and final wife.[6]
Growing up, Chaplin spent time in Spain, the United Kingdom, Switzerland and Cuba. She travelled often because of her mother's film career.[7][8] She started dancing ballet,salsa andflamenco at an early age.[8][9]
In 2025, Chaplin co-starred inAvatar: Fire and Ash, directed byJames Cameron, as the villainous Varang.[14][15] On casting the relatively unknown Chaplin, Cameron explained: "There was something [Chaplin] just locked into. There’s a sexuality; there’s a dominating psychology, and there’s a lot of fury. There are a lot of layers to what she’s doing there and the forces that are driving her. Oona was able to move fluidly back and forth between those in a way that I wasn’t seeing with the others."[16]
^Ross, David (28 April 2009). "Students step back in time to celebrate 75 years: Pupils and staff make it a special 1930s anniversary for Gordonstoun school".The Herald. p. 3.
^Thynne, Jane (30 July 2003). "Parents: Just like mum: Choosing the same career as a parent is very common – but not necessarily a good idea".The Guardian. p. 14.