Gerard Johnstone is a New Zealand screenwriter and director. He is known for the comedy sitcom series The Jaquie Brown Diaries and the horror films Housebound and M3GAN.

Johnstone was born in Invercargill, New Zealand, where he attended Verdon College. In the early 2000s, Johnstone and Jaquie Brown worked together at C4. A few years later, they created a production company, Young, Gifted & Brown, to make the New Zealand sitcom The Jaquie Brown Diaries, based on a satirical fictionalised version of Brown. It began airing in 2008 with Johnstone serving as writer and director.