While studying for the bar, Joy submitted a sample script for the ABC fantasy comedy-drama series Pushing Daisies. A friend passed the script along to a television producer, helping her get the job as a staff writer in 2007. She went on to become the only female writer on the USA Network crime drama series Burn Notice. She later served as a co-producer on the series.

Joy graduated from Stanford University and worked as a consultant at McKinsey & Company in Los Angeles before attending Harvard Law School. Joy was admitted to the bar in 2009 and practiced law in California prior to her career in entertainment.

In 2016, Joy co-created the HBO science fiction series Westworld and serves as its co-showrunner for up to six seasons. The series focuses on “a futuristic theme park gone wrong where robots start rebelling against humans”. The series went on to become one of the most popular series on television. For her work on the series, Joy earned nominations for the Primetime Emmy Award for Outstanding Drama Series and Outstanding Writing for a Drama Series, among others.