Leigh Whannell (/ˈli ˈwɑːnɛl/; born 17 January 1977) is an Australian screenwriter, actor, film producer, and film director. 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 made his directorial debut with Insidious: Chapter 3 (2015), and has since directed two more films, Upgrade (2018) and The Invisible Man (2020).

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 character in three of the installments. He was also the writer of the Saw video game (2009), and co-writer of the 2014 film Cooties.