Reza began work as an actress, appearing in several new plays as well as in plays by Molière and Marivaux.

In 1987 she wrote Conversations after a Burial, which won the Molière Award, the French equivalent of the Laurence Olivier Award or the Tony Award, for Best Author. Following this, she translated Kafka's "The Metamorphosis" for Roman Polanski and was nominated for a Molière Award for Best Translation.

Her second play, Winter Crossing, won the 1990 Molière Award for Best Fringe Production, and her next play The Unexpected Man, enjoyed successful productions in England, France, Scandinavia, Germany and New York.

In 1995, Art premiered in Paris and went on to win the Molière Award for Best Author. Since then it has been produced worldwide and translated and performed in over 30 languages. The London production received the 1996-97 Laurence Olivier Award and Evening Standard Award. It also won the Tony Award for Best Play. Life X 3 has also been produced in Europe, North America and Australia. Screenwriting credits include See You Tomorrow, starring Jeanne Moreau and directed by Reza's then-partner Didier Martiny.

In September 1997, her first novel, Hammerklavier, was published and another work of fiction, Une Désolation, was published in 2001. Her newly-published 2007 work L'Aube le Soir ou la Nuit (Dawn Evening or Night), written after a year of following the campaign of Nicolas Sarkozy has already caused a "sensation" in France.

On 24 November 2007 her play Le Dieu du Carnage, (The God of Carnage) directed by Jürgen Gosch and performed first in Zürich, received the Viennese Nestroy-Theatreprize for the best German-language performance of the season. It opened in London in March 2008, directed by Matthew Warchus in a translation by Christopher Hampton starring Ralph Fiennes, Tamsin Greig, Janet McTeer and Ken Stott. The London production won the Laurence Olivier Award for Best New Comedy, which Hampton accepted on her behalf. Hampton told the audience that Reza would be "thrilled" by the win.. The play premiered on Broadway with an opening night cast of James Gandolfini, Jeff Daniels, Marcia Gay Harden, and Hope Davis. God of Carnage won Best Play at the 2009 Tony Awards.

Plays

• Conversations après un enterrement (Conversations After a Burial), 1987
• La Traversée de l’hiver (The Passage of Winter), 1989
• « Art » (Art), 1994
• L’Homme du hasard (The Unexpected Man), 1995
• Trois versions de la vie (Life X 3), 2000
• Une pièce espagnole (A Spanish Play), 2004
• Le Dieu du Carnage, 2006 (God of Carnage)

Novels

• Hammerklavier, 1997
• Une désolation (Desolation), 1999
• Adam Haberberg, 2003
• Nulle part, 2005
• Dans la luge d'Arthur Schopenhauer (On Arthur Schopenhauer's Sledge), 2005
• L'Aube le soir ou la nuit, 2007

Screenplays

• Jusqu'à la nuit, (Till Night) 1983 (she also acted in this)
• Le pique-nique de Lulu Kreutz (Lulu Kreutz's picnic), 2000

As actress

• Que les gros salaires lèvent le doigt ! (Let the Fat Cats Lift a Finger!)1982 (as a chambermaid)
• À demain (Till Tomorrow), 1991
• Loin (Faraway), 2001