Leigh Whannell (born 17 January 1977) is an Australian screenwriter, producer, director, and actor. He is best known for writing films directed by his friend James Wan, including Saw (2004), Dead Silence (2007), Insidious (2010), and Insidious: Chapter 2 (2013). Whannell has directed two films, Insidious: Chapter 3, released in 2015, and Upgrade, released in 2018.

Whannell and Wan are the creators of the Saw franchise. Whannell wrote the first installment, co-wrote the second and third installments, was producer or executive producer for all the films, and appeared as the "Adam Stanheight" character in four of the installments. He was also the writer of the Saw video game (2009), and co-writer of the 2014 film Cooties.