Waititi won an Academy Award earlier this year for World War Two film Jojo Rabbit, and is also known for making Marvel's Thor: Ragnarok.
He will write the unnamed film with Scotland's Krysty Wilson-Cairns, who was nominated for an Oscar for 1917.
Meanwhile, US writer Leslye Headland is creating a new series for Disney+, the service's fourth small-screen spin-off.
The Mandalorian is already streaming, and gave Waititi his introduction to the Star Wars universe when he directed the series one finale and voiced the droid IG-11.
New series are also being made for Disney+ about Obi-Wan Kenobi and Cassian Andor.
On the big screen, other Star Wars movies currently planned include a trilogy masterminded by The Last Jedi director Rian Johnson; and another spin-off created by Marvel Studios boss Kevin Feige.
The news was released on "Star Wars Day" - May the fourth.