On stage, Casar's work includes the Almeida Theatre production of "Aunt Dan and Lemon"; the title role in "Hedda Gabler" at Le Petit Théâtre de Paris; and Olivier Py's 2009 production of "Les Enfants de Saturne" at the Theatre National de L'Odéon, Paris. In 2011, she appeared in the title role of Petra in "The Bitter Tears of Petra von Kant", and received critical acclaim in Arthur Honegger's "Jeanne d'Arc au bûcher" at the Barbican Centre with the London Symphony Orchestra.